Police and intelligence services do not believe that the four bombers conceived, planned and carried out the atrocity without help but as yet no one has been arrested.

Charles Clarke conceded yesterday that the intelligence services “know only a part of the full story and the challenge they have is to know more of the full story”.

Five months on from the attacks, agents are still not sure whether an explosives expert was sent to Yorkshire to help the four to assemble the rucksack bombs. Nor do they know why primed devices were left in the mens’ hire car at Luton railway station, suggesting that there should have been a fifth bomber.

The “narrative” that the Home Secretary wants published on the progress made will chart the bombers’ travels to countries such as Pakistan and Saudi Arabia in the months before the attacks but will not say why they went there or who they met. One reason is that the co-operation that friendly governments promised in the days after the attack largely dried up. Some of the countries suspect that Britain might try to blame foreign extremist groups for providing the inspiration, expertise and finance for what they argue was a homegrown operation.

At home, for all the excellent response from the Muslim community and Islamic leaders in the Leeds area, youngsters who attended Mohammad Sidique Khan’s youth club remain hostile to police. Detectives have yet to identify some of the visitors who dropped into Khan’s makeshift gymnasium in the basement of a mosque in Hardy Street, Beeston. Police believe that this is where the 30-year-old former teaching assistant recruited his team, but there are reasons to believe that the youngest, Hasib Hussain, could have been a latecomer. If so, it suggests that Khan’s first choice dropped out and is on the run. When Khan, Shehzad Tanweer, 24, and Jermaine Lindsay, 19, travelled to London on a reconnaissance mission on June 28, 18-year-old Hussain was not with them.

The teenager’s erratic behaviour on the day — which saw him wandering through a McDonald’s restaurant at King’s Cross station long after the others had detonated their devices — has never been explained and probably never will be. Experts believe that he may have been the last to know that they were undertaking a suicide mission, and not just leaving the bombs on packed Tube trains. Khan knew what the plan was. He left behind a video statement declaring himself “a soldier” but there is still no definitive evidence where or when the video was made. Nor have agents identified who edited Khan’s film to include a statement from Ayman al-Zawahiri, al-Qaeda’s second-in-command, virtually claiming that they ordered the London attacks.

One senior officer close to the investigation said last night: “Because the terrorists killed themselves we will never know the answers to all the questions about them, but we believe there are people involved in this plot and we will go on looking for them. For starters we still don’t know who first radicalised Khan and the others.

“Nor do we know who decided the public transport system should be the target. We appreciate the families of those killed must be frustrated and want answers, but so do we. Everyone must be aware that if there are others in the 7/7 group still out there, then they may strike again and that must be our priority.”

The mother of one of the victims last night accused the authorities of treating relatives with “utter disdain”. Marie Fatayi-Williams, whose son, Anthony, 26, was on board the Tavistock Square bus, argued that a public inquiry “is the only real way that we can truly get things discussed and see for ourselves what happened and what lessons can be learnt”.

When Tony Blair rejected further calls by the families and some Muslim leaders for a full inquiry he could not tell them that this would jeopardise the trials of other suspected terrorists due to begin next year.

The need for detectives to work on these cases and to guard against further attacks means that police have not had the manpower that they would have wanted to investigate the 7/7 plot. The official line from Scotland Yard is that “significant resources” remain committed to this inquiry but the priority has to be uncovering other terror operations in Britain.

Sir Ian Blair, the Metropolitan Police Commissioner, hinted as much earlier this week when he said that police believed that they had discovered three more bomb plots since July. He could not give details because some of the suspected plotters have now been charged. Similarly, intelligence agents could not reveal all they knew about Khan before July 7 as this would prejudice the results of an important terror inquiry that has still to come before the courts.

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