SEPTEMBER 11: A date which will always send a shiver down the spine; a date which will always make us stop and think; a date which changed the world.

Today is a day to remember a catastrophic moment in history, and to reflect on what has changed - and what needs to change.

For all the unspeakable terrorism we had seen before, the September 11 attacks instantly made the world a more vulnerable place.

In a few explosive, unforgettable minutes, a comparatively tiny band of extremist bandits was seen to be able to bring the world's most powerful nation to its knees.

Suddenly, there were no boundaries. Anything was possible. Anyone could be a victim. No one was safe.

And for all America's military might, for all the bombing of the caves in the mountains of Afghanistan, retribution has proved to be out of reach.

One year on, the fate of Osama bin Laden remains a mystery. The only certainty is that the fear he left in his wake lives on in us all.

It is that overwhelming sense of vulnerability, and a determination to somehow rebuild the safety barriers, that has led to a changed America and therefore a changed world.

George W Bush is a different president than the one who woke up on September 11. And Tony Blair is a different prime minister.

In their eyes, the threat posed by rogue states and the terrorists they nurture must be eliminated with or without the approval of other nations. If that means bombing Iraq without United Nations support, that is highly regrettable but necessary.

September 11 hardened the resolve to act before it is too late. But when military action by the West becomes proactive rather than reactive, the world has become a very dangerous place indeed.

Will the destruction of Saddam Hussein's regime make the world safer or simply create more martyrs prepared to further destabilise the world in pursuit of their own fanaticism?

The truth is that until the running sore of the Middle East conflict between the Palestinians and Israel is somehow healed, we will not even begin to drain the swamp of terrorism.

We do not pretend to know the answers, but today is a day to think very hard about what happened a year ago - and what faces us in the future.