When I joined the police it wasn’t unusual to be called a Paki or “Ayatollah” to my face. Nowadays racists are smarter: it is easier to leave an anonymous message on the Crimestoppers telephone service saying that I am a burglar.

In 1999, soon after I joined the Met, someone did exactly that. No one mentioned any of this to me, probably because this sort of intelligence is routine.

If you are a black officer who is frequently in the media talking about racism, it is sadly inevitable that you attract all sorts of malicious complaints. Armed with this information, however, someone made the surprising decision that the best course of action would be to tap my phone at work and place me under surveillance. The decision to initiate covert surveillance was a big step because it implied that the trust between the Met and me had broken down.

This was Operation Bittern, named after a wading bird with a loud call. The male bittern, I discovered, is known for having many mates. Perhaps someone was having a little joke behind my back.

The investigators found no evidence of any criminal conduct to sustain Bittern. The best they could come up with was that I was married and yet had other girlfriends. Had they asked, I could have told them that my wife Natalie knew — and fully agreed with our lifestyle.

I had an unconventional marriage. Shortly after the birth of our third child, Natalie and I realised that we had fallen out of love. We decided not to get divorced but instead to live in the same house and bring up our children together. I slept in a separate room. We have both had sexual relationships with other people, about which we were honest to each other. While Natalie has met some of my female friends — and got on well with most of them — neither of us would bring a partner into our home or involve the kids. One day we would sell our house, divorce amicably and go our own ways — which is what has now happened.

Instead, the investigators assumed that I was seeing other women behind my wife’s back. This was probably not what Parliament intended when it passed legislation allowing police to conduct surveillance on career criminals about to commit serious crime. If this is justification for covert surveillance, we’re all at risk.

There were two more possibilities as to why I was singled out. One was that fellow officers felt threatened by my opinions and were apprehensive that I would soon be promoted and have real influence. Perhaps that is a more credible reason why they wanted to find out if there was anything hidden in my private life. On the other hand, perhaps they really found my behaviour odd, because I didn’t behave like them.

I wasn’t often in the pub, I didn’t eat with them because I couldn’t eat the canteen food, and I didn’t share the political views of many of them. The differences between Iranian culture and traditional British ways of doing things were magnified in my job.

The worst possible interpretation of Bittern was that someone wanted to learn more about the work we were doing at the National Black Police Association (NBPA). If that was the case, the best way would be to listen to its legal adviser — me. Many of my conversations contained legally privileged information that related to legal cases against the police brought by black officers whom I represented.

When, in January 2000, Nahid Darougeh wrote to the Met making serious accusations about me, it was the smoking gun that some of my colleagues had wished for. Nahid’s main complaint wasn’t that I was corrupt as a police officer; it was that I had corrupted her daughter Mandy.

I had known Nahid for several months when I met Mandy, who was in her early twenties, studying law, and also Iranian. Mandy and I had a brief relationship. When I met her she had been very much in the shadow of her mother. During the time I knew her, perhaps partly through my influence, she became more independent. When she finished her degree she told her mother that she didn’t want to become a solicitor, and instead took a job at a café owned and run by a friend of mine. Her mother didn’t approve and neither did I. I thought she shouldn’t have given up on the law so soon.

My relationship broke down: first with Nahid, then with Mandy. We argued on the street: one of those furious, stupid, relationship-ending arguments that you sometimes can’t avoid. I jumped in my car and drove off. Later that night she phoned and we argued for another 20 minutes, both of us swearing and threatening, before she hung up. She was outside my house, when my arrangement with Natalie was that we would never bring our relationships home. This was the first time that this had become a problem.

A red mist descended. I phoned her three times and ranted into the phone, which was on voicemail. I said some terrible things: “I will take such revenge on you that like a dog you will be sorry. From now on you are dead. You think it’s a bluff. I give you an hour and see what I will do to you,” I shouted. Each call wound me tighter. “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. I’m ashamed. It was vile, inexcusable language to use to someone. I’m sorry now. Since then, Mandy and I have met for coffee, patched up our differences and become friends; it’s in the police surveillance logs.

But unknown to me, Mandy had kept the messages and at the time had shared them with her mother.

On January 28, 2000, Nahid’s letter went to the borough commander’s office, to Chief Superintendent Stephen Otter (now the Deputy Chief Constable of Avon and Somerset). She was interviewed that day, and on January 3 Supt Barry Norman, DS Wilkinson, one of the officers who had worked on Operation Bittern, and Chief Supt Otter taped Nahid making accusations. They were excited about this information: they did not want to get anything wrong.

They recorded her as she told them that I was a spy for Iran, that I had beaten up the new boyfriend of an ex-girlfriend, and that I had stolen her son’s jumper. The PSI [phone tap] was put back on my work telephone, and Operation Helios — the codename for the investigation into me — had begun.

My codename, Mozart, appears in many of the 2,288 statements, 1,670 exhibits, 2,054 documents and 2,196 actions of Operation Helios; many of those actions were taken in the year that it ran in secret, while I had a dim idea that something odd was happening but no conception of how every movement and call was being monitored. As I was struggling to comprehend why my fellow officers had taken to hanging around in the corridor outside my office, a surveillance team had taken up residence across the street.

Up to 44 officers were involved in Helios. As well as the phone tap and the surveillance, my emails were read and my work diary was examined. Although the law made it difficult for the investigators to listen to my mobile calls — that level of intrusion requires the Home Secretary’s authority — they examined the phone records to see whom I had called, who called me and for how long we spoke. They used cell site intercepts to follow my movements. My mobile phone was, effectively, a very expensive tracking device. I don’t know whether they actually tapped my home phone and mobile phone — they still don’t have to disclose that information to me — but my intuition is that they did.

They looked into my bank accounts and examined how much I was withdrawing and depositing to see whether I had secret accounts. My brother’s bank account, my wife’s and my father’s accounts were all looked at without their knowledge.

Later the surveillance was stepped up. I was photographed and videoed as I went back and forth from my house. Secret audio recordings were taken. Sadly, they were of such poor quality that the Helios officers needed to send them to the BBC’s sound experts to be enhanced — and when they failed, the British Secret Services were employed for the same task.

Late in 2000 I notice that a new guy is hanging around in the gym. His name is Billy. He likes to engage me in idle chat, which to be honest is distracting and irritating. Every day when I go to the gym changing room, there he is in his big sweatshirt. Every time I work out, there he is again, trying to chat, still in his sweatshirt.

I didn’t know what to make of Billy. Then I decided that maybe he was gay, and flattered myself that he must be interested in me.

One day, Billy introduces a new topic of conversation. He has just bought a dodgy car. He suspects the seller. What should he do? “Get a lawyer,” I said, and that was that.

Unknown to me, I had passed an integrity test. Billy was an undercover police officer, recruited from the West Midlands force to lure me into admitting my criminality. His bulky sweatshirt hid a microphone so that he could capture the moment. For two months I was subjected to his inane banter, until the investigators presumably gave up and sent him back to the Midlands.

If I had no idea at the time that Billy was a plant, I had even less idea that I had already passed two integrity tests earlier in the year.

Billy was small-time stuff compared with the operation mounted in May and June 2000. It took in the Los Angeles Police Department (LAPD), the FBI, the US Drug Enforcement Agency and the Royal Canadian Mounted Police, and gave a couple of Helios officers a nice trip to America to set it up.

Norman wrote a letter to the FBI and the LAPD showing that they were planning covert surveillance while I was in Los Angeles to give a speech.

On May 12, Supt Norman flew to the US to discuss using an undercover officer to trap me. Could I be secretly masterminding an operation to import steroids and fix visa applications? If so, this was the time to find out. He also visited Canada on the trip, because the Royal Canadian Mounted Police had found two Iranian officers who could work under cover in the US.

Next, two undercover officers, one male and one female, visited Kensington to become accustomed to the area. They lived in a flat that cost £100,000 a year to rent, had a budget of £150 a day for entertainment and received an extra £100 a day on their salaries — plus overtime — for the strenuous job of visiting restaurants and being trained in the Met’s covert operation procedure.

In November I attended the conference in Beverly Hills. My speech went well. At the coffee break an Iranian guy came up to me. He was living in Canada, he said, but he’d love to get a visa for the UK. What was Kensington like? I engaged him in a bit of light conversation. He was trying to sort out some offshore accounts, he said suddenly. How could he lose some surplus cash?

What? I tried to lose him. He followed me around. I told one of the other delegates that this guy was becoming a pest.

In a room near by, Supt Norman was following the progress of the sting. It wasn’t going well.

Part two of the operation was to introduce the beautiful female who would be a honey-trap for me. She never showed up.

The integrity test was an expensive failure, much like the rest of Operation Helios. Looking through the documentation of my case, the most surprising example of a failure to control Helios was a meeting that I nicknamed “the Windsor summit”. On December 5, 2000, the Met decided that soon I would have to be told about the investigation, and that it needed a new strategy.

On December 20, three deputy assistant commissioners, a number of chief superintendents, lay advisers and representatives of the Independent Advisory Group and senior members of the Met’s Department of Public Affairs led by Chris Webb, its deputy director, checked in to 24 rooms at a four-star hotel in Windsor. At a reception that night, over sherry and champagne, they discussed my case before going to dinner.

The next morning they heard a review of the operation so far by Supt Norman.

Did it give them comfort? When my defence team and I read the minutes of the meeting, it seemed to us that there was an air of desperation. Not surprising: a year had gone by and they were still not sure whether they even had enough to arrest me.

At the end of the meeting they decided on a strategy: go for everything. And on January 18, 2001, the day I was suspended, they went for it.

Fighting for my name

I walked out of the Old Bailey as a free man. I gave my one prepared line to the reporters who crowded me, making me feel like David Beckham. “I feel absolutely relieved and delighted that I have been unequivocally acquitted of all the allegations that have been made,” I said, leaving the stage to my defence counsel, Michael Mansfield, QC, who delighted in telling the waiting reporters that “what has happened is of almost Orwellian proportions”.

While the media feasted on the details that reporting restrictions had denied them for so long, there was still an unresolved problem: what to do with me.

The NBPA and my friends in the police wanted me to go back to work. I wanted that, too. I had spent my life as a police officer and I still loved the job, even though I was beginning to forget what it was like to do it. My Iranian friends, and my wife Natalie, had long since lost any confidence in the police and urged me to take a pay-off: it would be calculated on how many years of service I would have lost and my probable finishing salary. The amount was estimated by my advisers to be between £1.5 million and £2 million. To do that, I would have to go back to work for one day, shake the hand of the Commissioner to show that there were no hard feelings, and resign the next day.

I couldn’t do it. I wanted my job back. I was prepared to accept “words of advice” on two of the outstanding disciplinary proceedings: my call to Mandy, and the way I dealt with the location of my car when it was scratched — a form of censure in which I would concede that I’d made mistakes — because that was fair. The Met would drop the remaining eight.

At the last minute, when we thought we had a deal, it broke down. If I was going to return to work, the Met wanted me to work under the terms of a “service confidence agreement”. I wouldn’t be able to deal directly with members of the public. I wouldn’t be able to manage staff. In my mind, I wouldn’t be able to do any useful job. A service confidence agreement is used to rehabilitate officers who have been found to have committed serious breaches of police professional standards. It was totally out of proportion to anything that I had done.

And so on October 8, 2003, the NBPA told black Britons not to join the police. It would not just boycott all the Met’s activities to recruit officers from ethnic minorities, it would actively campaign to stop the Met recruiting black officers.

There was going to be a protest march on November 17 — but not just any march. A thousand black police officers would take the day off to march through Central London, in uniform, to New Scotland Yard. This was, by any standards, a crisis. The Home Secretary called for more talks “as a matter of urgency”. The Mayor of London called the escalation “dangerous”. The Met was “extremely concerned”.

That’s when the Home Office called on Acas.

The Advisory, Conciliation and Arbitration Service was founded in 1975 as a way for employees to resolve problems, but it is best known for trying to resolve large-scale industrial disputes such as the miners’ strike of the 1980s. There was no precedent for it to get involved in a police staffing issue, but we were all desperate. With the help of the negotiators we got a deal: no service confidence agreement. A return to work, my job back, disciplinary charges to be dropped, £60,000 in compensation and a promotion to chief superintendent three years after I earned it. I would finally get to go on the senior command course. The NBPA would lift its boycott and postpone the march.

On October 28, 2003, I walked back into work for the first time since January 18, 2001. The Commissioner, Sir John Stevens, announced that I returned with my integrity “demonstrably intact”. I had a new uniform — I had torn up my old one in anger years ago. I had a new job; and from the first moment I arrived back, I had the complete and unwavering support of the officers around me.

A couple of weeks later I attended the annual meeting of the Metropolitan Black Police Association. As I waited outside, I spotted the Commissioner entering the building by a different route. It would have been awkward for him to bump into me outside the Mayor’s office, in full view of the press. Inside, he spoke to the delegates. Then, spotting me in the audience, he turned to me. “Ali, I respect you for what you have done,” he said.

It was over.

© Ali Dizaei 2007: Not One of Us, by Ali Dizaei and Tim Phillips, is published by Serpent’s Tail on March 12 at £16.99; available from Times BooksFirst for £15.29: 0870 1608080; www.timesonline.co.uk/booksfirst