The war on terrorism came right into the middle of my parish here in the City of London on Sunday.

Streets were cordoned off as hundreds of police and firemen staged a huge exercise in which it was pretended that a terrorist had released a deadly poison in Bank Tube station.

I can't really complain: the upheaval didn't inconvenience us much at St Michael's - although some of the Christening party were a bit late.

Afterwards members of the congregation went up to the barricades and videoed the chemical warfare experts as they emerged from the Tube in their funny suits which made them look like Tellytubbies.

The public mood has changed in the two years since Saudi Arabian Islamic militants crashed airliners into the Twin Towers, killing more than 3,000 innocent people. Then there was overwhelming support for Mr Blair's and President Bush's campaign to hound, arrest - or kill - the perpetrators and to use every means possible to frustrate their evil schemes.

Now, after the wars in Afghanistan and Iraq, many people are not so sure about this aggressive policy. And the long-running soap opera called The Hutton Inquiry seems to be uncovering murky facts about the operations of our intelligence services and of the Government itself. The looming question in everyone's mind is: "Did we fight these wars on false pretences?" After all, no weapons of mass destruction have yet been found in Iraq and terrorist atrocities show no signs of abating. People are beginning to wonder whether the war on terrorism is simply making matters worse.

As we approach the second anniversary of September 11, it's worth reminding ourselves of why we should continue and intensify the war on terror.

When Saddam Hussein was in power, he used Iraq as a place where terrorism was organised and sponsored. Now in the chaos which has followed his deposition, Saudi and Iranian terrorists are flooding into Iraq to make sure that the country remains unstable, the perfect breeding ground for groups such as al Qaida. These terrorists will continue to kill as many westerners in Iraq as they can in the hope that public opinion will turn against the occupation and that the Americans and the British will get out.

Should we admit, then, that it's all been a ghastly mistake and withdraw? No. Iraq can be truly liberated and democratised - indeed this process is well under way already. And that is precisely why the terrorists are becoming even more frenzied. They are desperate. The terrorists themselves are terrified at the prospect of a free, democratic and prosperous Iraq in the middle of a vast area in which every other country is a repressive dictatorship.

We can transform Iraq into something decent. But it will take a long time. In an earlier age Rudyard Kipling referred to the sort of responsibility we now have in Iraq as "the white man's burden". That sort of language may be out of date, but the responsibility remains the same: to turn despotism and barbarism into civilisation.

* Peter Mullen in Rector of St Michael's, Cornhill, in the City of London, and Chaplain to the Stock Exchange.