Leading article: Time for the debate we have avoided since last July

This week Britons will mark the anniversary of the bombing of their capital. It will be a solemn moment in the life of the city, even such a city as London, which has endured many outrages in living memory, from the Blitz to the IRA campaigns.

Apart from focussing attention on the agony of the survivors, some of whom are still seek compensation, Friday's events are bound also to raise the question of whether it will happen again.

The Government has acted to pre-empt that concern over the past year, mainly by announcing new law upon law in its "war on terrorism". Right now, the Chancellor, Gordon Brown, is said to be engaged in a fresh attempt to increase detention without trial to 90 days.

Tony Blair, who likes nothing better than to sound tough, has sold this series of restrictions on civil liberties in a cannily populist fashion, marketing them as a common-sense response to irrevocably changed security circumstances, which only a group of fuddy-duddy liberal judges don't appear to understand.

This version of events won't, or shouldn't, wash. As Parliament's Foreign Affairs Committee highlighted at the weekend, the Government's much vaunted anti-terror initiatives, backed up by high-profile police raids, have failed to achieve what they set out to do - to diminish the risk to Britain from the al-Qa'ida network. Instead, so the MPs reported, the chances have grown since last year of another attack by al-Qa'ida, whose supporters, the report said, now posed a "serious and brutal threat".

That sobering judgement ought in itself to raise profound questions about whether the Government is going about combating terrorism in the right way. What is more significant, however, is that the committee has directly linked this growing threat to the war in Iraq and the incarceration of suspects in Guantanamo Bay, which it said had undercut the West's moral authority in combating extremists and had handed them invaluable propaganda. It all ought to make the Government sit up and think. Alas, it will probably do no such thing, for the Blair administration has made a point of never admitting the slightest connection between Britain's involvement in Iraq, or its slavish support for US policy in the Middle East, and the radicalisation of Islamic opinion at home. No doubt ministers fear that were they to accept such a link, they would expose themselves to the charge of partial responsibility for the London bombings.

Mr Blair moved to quash any discussion along those lines right at the start, saying just after the July events that it was an "obscenity" even to suggest that concern for Iraq had motivated any of the bombers. The Home Secretary, John Reid, returned to the same theme recently, remarking that none of the bombers mentioned Iraq in their wills or testaments. This has been an effective strategy for ministers, for by suggesting that those who discerned a link between the bombings and Iraq were somehow justifying their actions, they instantly muffled any public debate on those links.

It is to be hoped that the latest MPs' report will help end this year-long silence. It may have protected Mr Blair's flank but it has arguably served the wider public rather less well.

As the death toll from the war rises each week in Iraq, and now also in Afghanistan, it is more apparent than ever that we need a rational discussion on whether our continuing role in these conflicts has, or has not, fuelled Islamic extremism in Britain, enabling preachers of hate to seduce some who otherwise might not have come into their orbit. After Friday's ceremonies are over, that would be the right way to acknowledge this tragic anniversary.