Yard chief proved right over fears we are target

He said it was inevitable and now, it seems, he has been proven right.

Scotland Yard Commissioner Sir John Stevens's dire warning that Islamic terrorists would attempt to attack Britain came just two weeks before today's arrests.

After the Madrid bombings - an atrocity which was a wake-up call to Europe that al Qaeda was willing to strike - Sir John said: "There is an inevitability that some sort of attack will get through. My job is to make sure that does not happen."

His outspokenness sparked a bitter row with Home Secretary David Blunkett, who accused England's top police officer of making people "jumpy".

Mr Blunkett said: "There has to be a balance between telling the truth and reassurance."

But today, as forensic science experts examine what they believe are the same sort of explosives which were used to devastating effect in the Bali bombing, Sir John's uncomfortable truth-telling seems far wiser than the sort of secrecy Mr Blunkett would prefer.

Sir John, and Scotland Yard's other senior officers, have concluded that only by being open about the scale of the threat will they be able to get the public acting as "eyes and ears", providing the sort of tip-offs which could be the key to cracking tightly-knit terrorist cells that MI5 and MI6 have so far failed to infiltrate.

Today's raids also raise the frightening new spectre of an enemy within - British citizens prepared to launch devastating attacks on their fellow citizens.

Until now, the vast majority of antiterrorist arrests have been of suspects who used the asylum system to gain entry to Britain, and that system's history of managerial incompetence to disappear.

But with eight British citizens now suspected of being involved in a terror plot, Sir John and Mr Blunkett have to face up to the even more devastating possibility that al Qaeda has recruited the perfect "sleepers" - British citizens operating as terrorists in their own country.

Police and security services now have to strike a delicate balance.

On the one hand they must attempt to infiltrate the almost-invisible world of an al Qaeda underground made up of British citizens hiding in their own communities; on the other, they must at all costs avoid alienating the huge Muslim community.

The FBI and CIA are still struggling to get co-operation from Arab-Americans after launching massive raids, intrusive surveillance and huge stop-and-search operations post-September 11.

Cool heads must now avoid repeating the same mistakes in Britain. The fight against terrorism around the world shows that gaining the help and cooperation of the Muslim community here is the only way to root out the al Qaeda threat.