Leading article: The lessons of 7/7

One year on from the bomb explosions on the London Tube trains and bus that claimed 52 lives, we still know terrifyingly little about how it happened and how likely it is to happen again. The reports that the security services let Mohammed Siddique Khan, the leader of the 7/7 bombers, slip through their fingers do not inspire confidence. The failure to put Khan under surveillance may not have been particularly culpable - it is impossible to assess how important he might have appeared compared to all the other possible threats. But that is the point. Unless there is an independent inquiry into the performance of the intelligence agencies in relation to 7/7, it will be difficult to know to what extent they failed to act on information as they should have.

So far, as we report today, the authorities seem to be unable to answer many of the most basic questions about the 7/7 bombings. The bland official "narrative" says only that "it appears" that the bombs were home-made, yet this is central to the question of whether the plot was the work of a closed cell or a wider network. Equally, it has taken a study by an academic outsider, Nafeez Mosaddeq Ahmed, to assess the extent of the bombers' international terrorist connections. He believes that they had extensive support from al-Qa'ida in Pakistan and suggests that MI5 knew about it.

However, this is emphatically not a matter of apportioning blame. It is much more important than that. What is vital is that the security services learn from what happened, and the best way of ensuring that they do is to subject them to some kind of external scrutiny. As Crispin Black, a former Cabinet Office intelligence analyst, writes on page 31, "most sensible people realise it is operationally vital for the intelligence services to keep their secrets". But the effect of such secrecy has been that the agencies are "slow and settled in their ways and outlook, almost like medieval guilds". Mr Black speaks from experience, and what he says accords with what is known from those occasions when the public catches an accidental glimpse of the inner workings.

He makes some sensible proposals for ways in which oversight of the security services could be improved without compromising the necessary cloak of secrecy, with a supervisory body modelled on the Bank of England's Monetary Policy Committee. Yet, unfortunately, the Prime Minister's political interests have been so tied up with those of the heads of the intelligence agencies since their joint venture in making the case for war in Iraq that he will not challenge their medieval guild mentality.

Since 11 September 2001, the war against jihadist terrorism has taken the wrong road at almost every turn. The undermining of human rights at Guantanamo Bay - now gradually being unpicked by the United States Supreme Court. The invasion of Iraq, which provided the jihadists with a new recruiting ground and which drained resources and attention from Afghanistan. And the feeble and error-strewn response to our own terrorist attack - from Stockwell to Forest Gate. The police tried to resist independent investigations of their mistakes in those cases, but at least they are forced to justify themselves to the Independent Police Complaints Commission. The security agencies are under no such discipline.

It may be, as they claim, that the security services and the police have prevented other terrorist outrages since 7/7. But until there is a better system of independent oversight of our intelligence agencies we can have no confidence that the mistakes of the past will be learnt from rather than repeated.