AT LEAST 400 Al-Qaeda terrorist suspects — double the previous estimates — are at large in Britain, according to police and MI5.

Dame Eliza Manningham-Buller, director-general of MI5, has said the figure could be as high as 600 if all those thought to have returned from combat training in camps in Pakistan, Afghanistan and elsewhere are included.

The new assessment — effectively a “terror audit” of Britain — was confirmed this weekend by one of Britain’s most senior police officers, who warned that shortages of trained surveillance teams were undermining attempts to monitor all the suspects.

“With about 400 terrorist suspects it requires a great deal of resources to investigate them,” said James Hart, police commissioner of the City of London, a prime Al-Qaeda target. “It’s impossible. You simply have to make intelligent guesses about who to watch. It’s a bit of a lottery.”

Hart’s words carry weight because he helped co-ordinate the response to last July’s terror attacks in London. He is also on a committee of security chiefs responsible for protecting the capital from future attacks.

The figure of 400 has emerged from a reassessment by MI5 of the terrorist threat after the July 7 suicide bombings, which killed 52 innocent people. It is double the number of suspects that Lord Stevens, the former Metropolitan police commissioner, said last year were potentially able to carry out attacks in Britain.

The Joint Intelligence Committee of security chiefs has already warned that Al-Qaeda’s campaign against Britain and other western countries has been “energised” by the war in Iraq. Police chiefs now believe this will last at least 20 years.

Officials say the 400 include a “hard core” of between 40 and 60 trained fighters with the capability and the intention to carry out attacks in Britain.

There are other Islamic extremists “around the edges” of the 400 who could become active terrorists at any point. MI5 has already admitted it failed to follow up evidence that the July 7 ringleader Mohammed Siddiqui Khan was involved on the fringes of a terrorist plot.

In addition, MI5 has drawn up a “thermal map” of terror hotspots across Britain. The threat is said to be particularly acute in the Manchester area, where police have disclosed that several suspected would-be suicide bombers have been stopped at the airport en route for Iraq.

MI5 has received funds to open offices in Manchester, Liverpool, Leeds, Birmingham and Glasgow with others planned for Wales and the southwest.

But police say they are being hindered by lack of money. Hart said: “Discussions are going on about how more resources can be put into this project. There is not enough money being put into this. We should be doing much more. We are talking about the safety of the United Kingdom.”

Hart’s comments were backed by opposition MPs. Patrick Mercer, Tory spokesman for homeland security, said the government should act straight away to increase funding for counter-terrorism.

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