As a chief superintendent in the Metropolitan Police, Ali Dizaei spends much of his time discussing strategies and the finer points of law-and-order policy. Once a fortnight, however, he blocks out a day in his diary for “back-to-the-floor” patrol duties. It’s important, he believes, that senior ranks never lose their feel for what it’s like out there on the streets.

The day we meet is patrol day, and so it is that at lunchtime we find ourselves standing outside Costa Coffee in Hounslow while he struggles with the zip of the stab vest that is regulation wear for all officers. “I am relatively safe on the streets of Hounslow. But I wear it when I go into Scotland Yard,” he says, laughing. The Times photographer and I laugh with him, but there will be those who don’t find the joke so funny.

Next week is a big week for Dizaei. He recently went before a promotion board and on Tuesday he learns whether he will become a commander — a rank four steps away from commissioner. Then on March 12 his long-awaited book Not One of Us is published, telling the explosive story of the marathon investigation into him by officers of the Met. Many of the details are astonishing in their pettiness and jaw-dropping in their apparent malevolence.

Iranian-born Dizaei is a high-profile, politically active police officer who was once tipped to be Britain’s first black chief constable. By his own admission he can be flash, combative and arrogant. He rubbed people up the wrong way. The result was Operation Helios, a surveillance operation of breathtaking proportions that was mounted against him, ran for more than two years and cost the taxpayer what the Met says was £2.2 million but Dizaei would argue, when all the costs, including that of the trial, are taken into account, was £7 million. It led to Dizaei being suspended and accused publicly of being involved in drugs, using prostitutes, spying and corruption — grave allegations that proved to be wholly and ridiculously unfounded. In 2003 it culminated in bitter farce with Dizaei brought to trial at the Old Bailey on charges relating to matters so mundane that they beggar belief. His acquittal plunged the Met into its worst race relations crisis since the Stephen Lawrence inquiry.

Today Dizaei is borough commander for Hounslow, in West London. In the wake of Helios he was advised that he could have received a payoff of up to £2 million, but he says that he wanted his job back so he could help to tackle the sort of discrimination that he faced “from the inside”.

His beat covers leafy Chiswick but also some of the most densely populated immigrant estates in Britain. In some areas of Hounslow two-thirds of the population are nonwhite.

Dizaei boasts proudly that, with his 700 officers, he has turned it into one of the best-policed boroughs in the Met area, exceeding targets for detecting and reducing crime, and winning the support of the community. In a recent survey 85 per cent of residents said that they were satisfied with the service he and his team provide.

After three years in the job, though, he is ready for a fresh challenge. “I’ve done my bit for Hounslow,” he says, as we settle around the meeting-table of his office at Hounslow Central police station. “I want to go and deliver for a bigger Met.” He is “cautiously optimistic” about his promotion chances: “You cannot fault my operational competence.”

Yet he knows that, despite the acquittal and his exoneration in the exhaustive Morris inquiry that followed, there are those who still question him on a personal level. Part of the reason for his book is finally to “put the record straight” and let people know what he is really about. But the timing of publication so close to his promotion interview is, he insists, coincidence: “There are those who probably think that this is stage-managed, but it is not.”

Whatever the reality, it has certainly been no secret that he was writing his story. Indeed, it was part of the deal when he returned to work. He agreed to drop both his employment tribunal against the Met and a proposed BBC documentary, “but the book remained on the table”. His employers were offered a copy of the manuscript several months ago “but they didn’t want to see it. Now there are sensitivities, which surprises me.”

Not One of Us is not about the Metropolitan Police Service, he says, but about a handful of officers who he believes set out to destroy his reputation and career: “My accusers would love to hide behind the corporate identity of the Met but I am not going to give them that privilege. Any organisation should be big enough to criticise itself in order to move forward.” This is true, but the fact that these individuals — he dubs them “the self-appointed knights of integrity” — were able to operate under the aegis of the Met will not inspire public confidence.

Among the high-ranking officers Dizaei is critical of are his then boss, Superintendent Stephen Otter, now the Deputy Chief Constable of Avon and Somerset, who gave evidence against him at the Old Bailey. But he reserves his most scathing words for Chief Superintendent Barry Norman, who headed the 44-strong CIB3 (Complaints Investigation Branch) team and is now borough commander for Islington.

Helios was a monumental operation that generated 2,288 statements and 1,670 exhibits, but such brain-numbing detail does not prevent Dizaei’s narrative from being a gripping read. There are Clouseau-like vignettes but also sinister moments that shudder with all the tension of a John Grisham novel. We learn how his phone was tapped, his e-mail monitored, his bank accounts and those of his brother and father scrutinised. A surveillance team set up residence across the street from his office, a secret camera videoed him outside his home and undercover officers tried to befriend him as part of ham-fisted “integrity tests” that would have been laughable had they not been so serious.

Dizaei is forthright and quick-witted, but reading the book I found that there were several not particularly likeable aspects to him. He can be cocky, dogmatic and volatile. One of the factors that enabled investigators to build a case against him was a break-up with a girlfriend during which he left vile, menacing messages on her voice-mail. In his favour, he relates this episode — and many others — with brutal honesty against himself. Those who know him tell me that he is bold and flamboyant but also bright and charming. Perhaps the quality that comes across most when you meet him, though, is his unerring passion for his job.

Dizaei, now 44, believes that police work was his destiny. In Tehran, where he grew up, his grandfather had been assistant commissioner, his father was head of the traffic police and his uncles were also in the force. By the age of 4 he, too, wanted to be a cop.

His father, however, had different ideas. He wanted his two sons to become doctors or lawyers. A fervent Anglophile (he had visited the UK several times and once escorted the Queen and Duke of Edinburgh during a tour of Iran), he believed that their best chance of success was through a British education. So at the age of 10 Dizaei and his brother Hamid, then 9, were sent to a public school in Arundel, West Sussex.

They were smaller than the other boys and spoke no English. Dizaei says he lost count of the number of times his head was flushed down the loo. But puberty was kind to him. He filled out, became captain of the rugby team and learnt how to play tough. He also turned into “a bit of a bastard”. “There’s not much opportunity to be nice at boarding school and I became a product of the system,” he says. “Having to fight for everything means that you learn to fight for anything, and I developed a habit of pushing the rules as far as they could go.”

He was 17 when his formal schooling came to an abrupt halt with the Iranian revolution. His father, who had always struggled to pay the fees, could get no money out of the country and the Dizaei brothers were given a month to find alternative accommodation. They ended up in London, being passed between relatives and friends while they paid their way by working as waiters and washers-up in restaurants.

Dizaei says that those formative years turned him and his brother into “different animals”. “Hamid became withdrawn, reserved, softer — he just wanted to create his own bubble and find the kind of love he didn’t have as a child, and he has done that. I emerged as someone who was never content. My PA often says to me that I can’t live without a challenge, and it’s true.”

He blagged his way on to an HND business course by saying that he had restaurant management experience. From there he secured a place at City University Law School in London. He ran his credit cards to the limit to buy a black BMW: “I was flash, I was cool, I must have made some people laugh their heads off when I drove to my lectures on the one day a week I could actually afford petrol.” He also married a girl whom he had known for a month. It was all about “trying to fast-forward my life: to act like the successful guy that I wasn’t yet”.

He didn’t make it as a barrister. A one-year course at the Inns of Court exposed him for the first time to “the Establishment”. He found that he didn’t have the education or the smoothness to fit in “and being Iranian — a Muslim — wasn’t the best start”. His father was upset but as far as Dizaei was concerned, it left him free to do what he had always wanted.

Dizaei spent the first 14 years of his police career with the Thames Valley force, where his colour was an issue from the first day. Despite being the only nonwhite in his probationer intake, he was also the only one to be housed on the Whitley estate in Reading, known locally as a British National Party heartland. When he returned home to find “Pakis out of Britain” painted on his front door, he bought himself a dobermann. He was nicknamed Ayatollah, and colleagues joked openly about his “smell”. After three weeks of hostility, he says, he nearly quit: “But those early days were reminiscent of my start at boarding school — every time I was pushed I wanted to fight back.”

He was tenacious and ambitious, studying for an MA and eventually a PhD in his spare time. Within seven years he was being fast-tracked to the rank of inspector, but he remained unpopular. The assistant chief constable who recommended him for promotion noted that “he should be kinder to people who are less intelligent than him”, and that “he has a tendency to alienate himself because of his ability to argue a point”. On his day of selection interviews, the group he was with voted him the most likely to be a future chief constable but gave him the least votes as someone with whom they would want to go on holiday.

Dizaei joined the Metropolitan Police as a superintendent in March 1999, having been invited to apply by the commissioner, Sir Paul Condon. It was the year in which the Met was found guilty of institutional racism after the inquiry into police handling of the murder, six years earlier, of Stephen Lawrence, a black A-level student. Dizaei was by then vice-chairman of the National Black Police Officers Association (NBPA). Bringing him on board was a signal that the Met was going to tackle racism head-on.

If you are a black officer who is quoted frequently in the media about racism, says Dizaei, you attract malicious complaints. While he was at Thames Valley an informant had claimed that he was fixing speeding tickets and mixing with a drug dealer. Both allegations were baseless; Sir Paul Condon knew of them and had dismissed them. Within months of Dizaei joining the Met, however, someone else left an anonymous allegation on the Crimestoppers answer machine that he was a burglar. This turned out to be enough for the Met to get a private side intercept — a tap — on his phone line.

Dizaei does not say that this surveillance was racially motivated, but it coincided with rapidly souring relations with fellow officers at Kensington, where he was stationed. They resented the fact that he had been given a car-park space in the yard and that he took time out to attend NBPA meetings. According to Dizaei, his boss, Chief Superintendent Otter, made it clear that he didn’t like him drinking tea from an BPA mug or wearing an BPA tiepin.

It is easy to see how Dizaei’s trenchant manner may have irritated others, but it is impossible to justify what happened next. The covert investigation into him uncovered no criminal activity but did lead to the discovery that, although he was married, he had girlfriends. Dizaei deals with this by explaining that, eight years into his second marriage, he and his wife Natalie, a nurse, fell out of love and agreed to separate but remain living in the same house for the sake of their three sons.

The way he puts it, both were free to see other partners but they shared an understanding that any boyfriends or girlfriends would not be brought into the home. It sounds a bizarre arrangement. Dizaei points out it was “nobody’s business but mine unless it affected my conduct in the job”. It didn’t affect his behaviour at work but it did lead to a ferocious row outside it — which, in turn, led to Operation Helios.

Mandy Darougeh was an Iranian law student, in her early twenties when Dizaei had a brief relationship with her. When it ended, Mandy went to the house in Henley that Dizaei shared with Natalie and the children and spoke to him from her mobile phone. Both of them were swearing and threatening each other, and after she hung up, Dizaei says, a red mist descended. He called her back three times. When she didn’t pick up, he ranted into her voicemail. The quotes, all logged in the investigation against him, made choice reading: “’You want war, bitch, you’re going to get war. First I will start with your family and then I come to you and your reputation. I will spread all over London that you are a prostitute.”

Of course it wasn’t true. It was inexcusable behaviour, he says. “With 20/20 hindsight I should never have spoken the way I did.” They made up afterwards. But the apology was not enough. Mandy’s mother complained to his bosses and alleged, among other things, that Dizaei was an Iranian spy. To those who had already spent 18 months investigating him and drawn blanks, the accusation was, says Dizaei, “a gift from God”. But the spying accusation didn’t stand up. The accusation that he had had “inappropriate contact with prostitutes” turned out to be based on a conversation, recorded as part as the surveillance, in which a friend teased him that “the only girlfriends you get are the ones you have to pay for”. His suspected drug habit was based on equally fatuous evidence — yes, a nurse friend had supplied him with needles, but they were for his mother, who has to have regular painkilling injections for arthritis and does not have access to good needles in Iran. A charge that he had pocketed cash after booking flights to America through a travel agent he knew was quietly dropped, as were the other serious allegations levelled at him.

The eventual case brought against Dizaei was based on a foolish lie. In September 2000 his car was vandalised outside Kensington police station. Dizaei discovered the damage before he drove off to an afternoon meeting of the NBPA but he didn’t report it until he got back three hours later. He didn’t want his fellow officers to know that he had been to the meeting — his boss, Chief Superintendent Otter, had already told him that he should spend less time on NBPA work and more time in his operational job: “So, looking for a quiet life, I lied.”

This untruth — saying the car had been parked all day — led to him facing trial for perverting the course of justice and misconduct in public office (charges relating to mileage expense claims were later dropped). The trial lasted for five weeks. Prosecuting counsel was Richard Horwell, QC, First Senior Counsel to the Crown; Dizaei hired Michael Mansfield, QC. “If QCs don’t defend cases involving scratched cars, it must be the first and will probably be the last time that the First Senior Treasury Counsel has prosecuted one,” he writes.

When Dizaei finally returned to work in October 2003, Sir John Stevens, the Commissioner, said that he did so “with his integrity demonstrably intact”. Dizaei “accepted words of advice” about the way in which he spoke to his ex-girlfriend Mandy, but all disciplinary charges against him were dropped. He received £60,000 in compensation and was promoted to chief superintendent. He was also given a place on the prestigious Senior Command Course — a course for which he had previously been singled out until Helios blew up in his face.

The Senior Command Course is designed to prepare Britain’s best police officers for the highest ranks. It involves six months of intensive 12-hour days and for Dizaei was clearly a huge personal, as well as professional, learning curve. “Finally,” he acknowledges, “I learnt lessons that had probably held me back since schooldays.”

Chief among these was humility, “a lesson that my colleagues would consider was overdue,” he says. “I was arrogant, too forceful in debates, and what Helios and the command course taught me was that you are not always right, how to say sorry, to concede a point. Being more human, softer, has always been a challenge to me because of my upbringing. But I have had my judgment day, and the positive side of that is that you see your shortcomings.”

He says that he no longer resists “canteen culture” — shorthand for the camaraderie between coppers — in the way he did. “As a borough commander I have officers who do like to see me in the canteen. Before, I never used to go to leaving dos in pubs. Now I do. I have learnt to socialise and network. I find it hard and that is indicative of black and Asian officers generally — we are not very good at schmoozing. It’s partly cultural and it’s to do with pride, because schmoozing requires eating humble pie. The Muslim Asian culture doesn’t like that; it goes against the grain.”

I find this fascinating, I tell him, because I thought that Muslim culture was capable of being gracious and accommodating. “Yes, but not to people in a position of power who are not of your own kind,” he says. “That is the difference.”

This, of course, is the crucial point. Dizaei is not socially inept. You have only to spend a short time in his company to know that he is naturally gregarious. He makes good eye contact. He is articulate and urbane. His weakness, which surely stems from his childhood and the racism in his early police career, was always his chippiness.

He is keen to demonstrate that he has adjusted his personality, but also stresses that his lifestyle hasn’t changed. He still prefers a nightclub to a pub — he used to be a regular at Tramp — and sees no reason to apologise for this. Unlike some of his colleagues, he has a social circle that embraces a wide cross-section of society. He mixes with the Iranian community but also counts among his regular friends some of the men with whom he was at school. “These people are extremely wealthy now,” he says. “They are big players in the City and the legal profession. And it may be that your average cop doesn’t dine at The Ivy, but I’m afraid I do. I get invited not because I am a cop but because I am Ali Dizaei and we used to play cricket together when we were 12.”

He and Natalie are now divorced and no longer live together, which means, he hopes, that his children no longer have to see his girlfriend described in the press as a “mistress”. His sons are aged 20, 19 and 15 and were badly affected by what happened to him. “The eldest, especially, doesn’t trust the police at all. That’s a shame,” he says.

Dizaei regularly encounters the officers who investigated him. He often finds himself opposite Barry Norman in meetings at Scotland Yard. “I say hello to him, he says hello to me. I’m sure he is not going to send me Christmas cards and I won’t be inviting him to my son’s wedding. But we are professional. I had to come back with a view that I wouldn’t be bitter and twisted, because if I was I wouldn’t be able to do my job properly.” He believes that what happened to him is less likely to happen to someone else, and that there are now sufficient safeguards in place — “But no, I don’t feel safe talking on my mobile phone.”

In December the Investigatory Powers Tribunal, which is headed by a high court judge, found that the bugging of Dizaei’s phone during Operation Helios was unlawful. This is another vindication for him and another blow for the Met.

To anyone who may be wondering, Dizaei still harbours ambitions of becoming a chief constable. On the senior command course, which he completed in October 2004, he says he was marked outstanding in six of the ten competences — he lists them as leadership, resilience, working with others, communication, race and diversity, and community focus. “Interestingly, I am the only one of the ten participants on that course yet to be promoted,” he adds pointedly. So what does that tell him? “I am going to wait and see what the promotion board says.”

Dizaei’s story is one of great complexity but also of blinding simplicity. The discrimination that he experienced is deeply shocking but also utterly recognisable. We saw another interpretation of it recently on Celebrity Big Brother ; we all witness it subliminally in our everyday lives in multicultural Britain.

“By the year 2010 half of London is going to look like me, or slightly like me — Asian and black. That is a GLA prediction,” says Dizaei. “What we don’t want is the police that serves it to look like a pint of Guinness — all black at the bottom and white at the top.”

It’s a neat soundbite, but it is not the reason why the Met should promote him. Above all, we want our senior policemen to demonstrate leadership, courage, trustworthiness and sound judgment. Dizaei is not infallible. However, he has learnt from his mistakes and become a more rounded individual because of them. Despite being subjected to microscopic scrutiny, he has emerged triumphant. He is bright, innovative and unwaveringly determined. For the next rank, at least, he surely ticks all the boxes.

© Ali Dizaei 2007: Not One of Us, by Ali Dizaei and Tim Phillips, is published by Serpent’s Tail on March 8 at £16.99; available from Times BooksFirst for £15.29: 0870 1608080; www.timesonline.co.uk/booksfirst

1962 Ali Dizaei born in Tehran. His father and grandfather both in the police.

1986 Joins Thames Valley Police and rises fast.

1999 Transfers to the Metropolitan Police as a superintendent.

1999-2000 Investigated after allegations of corruption, using drugs and prostitutes, and spying for Iran.

2001 Suspended. 2002 Charged with perverting the course of justice, misconduct in public office and making false mileage expense claims. Admits lying to hide his attendance at a National Black Police Association meeting.

2003 Cleared and reinstated. Awarded £60,000 compensation.

2004 The Independent Police Complaints Commission calls the investigation, Operation Helios, “seriously flawed”. The official cost of the operation is £2.2 million but Dizaei estimates the true cost to have been £7 million.

2006 Dizaei criticises the Forest Gate raid and passenger profiling on aircraft.

2006 It is revealed that during Operation Helios his private calls were unlawfully tapped.