Mohammad Sidique Khan’s name featured twice in MI5 anti-terrorist operations more than a year before he went on to lead the 7/7 suicide attacks on London.

The revelations can be reported for the first time after yesterday’s conviction of Omar Khyam, a close associate of Khan, for plotting to build a 1,300lb bomb to blow up a crowded nightclub or shopping centre.

Far from being a “clean skin” Khan had been photographed, followed and bugged by intelligence officers more than a year before the July 2005 bombings that killed 52 innocent people and ranked as Britain’s worst act of mass murder.

Security sources told The Times that they had identified a “Sidique Khan” in 2004 as the owner of a mobile phone called by an alleged al-Qaeda financier and of a Honda car which was tailed from the SouthEast to Yorkshire by investigators. Despite those leads, which placed Khan firmly in the company of high priority terrorist suspects, he was not investigated further.

The disclosures fuelled demands for a public inquiry into 7/7 and raised doubts about the accuracy of assertions by John Reid in the Commons that none of the bombers’ identities was known to the security services before July 7.

The Home Secretary was speaking after Khyam and four other men received life sentences at the end of a year-long terrorist trial that cost an estimated £50 million and had a jury deliberating for a record 27 days before delivering its verdicts.

Sir Michael Astill, the trial judge, told the five men that they had “betrayed the country that has given you every advantage in life”.

The jury was not told that two men who met Khyam four times when he was under surveillance in early 2004 were Khan and Shehzad Tanweer, his right-hand man in the 7/7 cell. About 16 months later Khan, Khyam and two other men detonated suicide devices on three Tube trains – at Edgware Road, Aldgate and King’s Cross – and on a London bus.

Nor did the jurors know that Khan joined Khyam and other members of his bombing team at an al-Qaeda training camp in Pakistan in July 2003.

The two men were part of a group of young Britons who trained under and took orders from Abd al-Hadi al-Iraqi, the al-Qaeda leader who was transferred to Guantanamo Bay last week after being caught by American forces in Iraq.

Police believe another associate of the group tried to buy surface-to-air missiles to bring down a passenger jet. Kazi Rahman, 29, pleaded guilty last year to trying to buy terrorist weaponry and was jailed for nine years but his conviction can only be reported now.

Senior Pakistani intelligence sources told The Times that agents had monitored the group of “English boys” and alerted British agencies that they were planning to strike in Britain.

A high-ranking official said: “There is no question that 7/7 could have and should have been stopped. British agencies did not follow some of the information we gave to them.”

The connection between the convicted bomb plotters – who were caught in a huge investigation codenamed Operation Crevice – and the 7/7 bombers led to a growing clamour for a public inquiry.

Rachel North, who survived the King’s Cross blast, said she had been appalled to learn that Khan and Tanweer were associates of known terrorists.

“I remember that Charles Clarke [the former Home Secretary] came out and said ‘these bombings came out of the blue, these men are clean skins’,” said Miss North.

“It was tempting to believe that these guys had never been known to the police or the security services, that they had somehow managed to make these bombs and drive down to London and get on Tube trains and a bus, and that it was a terrible tragedy and there was nothing anybody could have done to stop them.

“When it transpired that was not the case, it was devastating. This has fuelled my desire for an independent inquiry because it appears we have not been told the truth about what we knew about these bombers prior to 7/7.”

A group of survivors will deliver a solicitor’s letter to the Home Office today demanding “an independent and impartial public inquiry” which would produce “a comprehensive, accurate and definitive factual account” of the events of 7/7.

The Conservative and Liberal Democrat front benches also called for an independent inquiry into the bombings and the suggestion that MI5 missed vital opportunities to prevent them. But Mr Reid rejected the call for a public inquiry, which he said would divert resources from the frontline fight against terrorism.

He told David Davis, the Conservative Shadow Home Secretary, he was “wrong” to claim that the identities of any of the bombers had been known before 7/7.

“They were not known to the security services until after 7/7,” insisted Mr Reid, who praised the police and security services for their work in foiling the bomb plot.

Mr Davis said last night that the Home Secretary’s position was indefensible.

He said: “The Home Secretary continues to block an independent inquiry into a major security failure that left 52 dead and 700 injured on the grounds that it is a waste of time.At the time of 7/7 we were told the suicide bombers were unknown to the authorities. This is plainly not true.”

Mr Reid told Parliament that MI5 had taken the unprecedented step of publishing a list of questions and answers about 7/7 on its website.

In its statement MI5 said: “Even with the benefit of hind-sight, it would have been impossible from the available intelligence to conclude that either Khan or Tanweer posed a terrorist threat to the public.”

Mr Reid said he had also asked the parliamentary Intelligence and Security Committee to reappraise its report, published last year, on the bombings. But Paul Murphy, MP, chairman of the ISC, said that the fresh disclosures did not change his view that there had been “no culpable failures by the security and intelligence agencies”.

Deputy Assistant Commissioner Peter Clarke, head of the Counter-Terrorism Command at Scotland Yard, said the conviction of Khyam and four of his accomplices marked a new understanding of the al-Qaeda threat to Britain.

Mr Clarke said: “The investigation showed the links that these men had with al-Qaeda in Pakistan. Most of them had attended a terrorist training camp in Pakistan in 2003, and were taught how to make explosives; some had been involved in extremism as far back as 2001. This was not a group of youthful idealists. They were trained, dedicated, ruthless terrorists who were obviously planning to carry out an attack against the British public.”

Mr Clarke said it was now known that Khan and Tanweer had met the Operation Crevice suspects but that they were judged at the time not to pose a threat to public safety.

He added: “It is a grave disappointment and a matter of great regret to everyone involved in counter-terrorism that we were not able to prevent the attack on 7th July, 2005. What this case and others in the future will show is that we are dealing with a threat posed by interlinked networks of terrorists.”

— Home-grown British terrorists regard themselves as part of “global insurgency” which poses a new threat to international security, said an official US report published yesterday. British intelligence chiefs have confirmed to The Times that they are worried by the prospect of the next attack in America being committed by a UK citizen arriving without hindrance in the US on the visa-waiver programme. They are liasing with the FBI to identify possible suspects.

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