LONDON, Dec 9: Security services have thwarted a planned attack on London similar to the March 11 train bombings in Madrid by extremists, the British capital's police chief said on Thursday.

"Thank God to date, and we have had to work extremely hard, we've thwarted attacks," Metropolitan Police Commissioner Sir John Stevens told the BBC. Asked if his force had stopped a strike on the scale of the Spanish attack, he added: "Yes, I can't discuss it because of court proceedings - but yes we have stopped a Madrid."

The morning rush-hour bombings on commuter trains killed 191 people in the most devastating attack in modern Spanish history, just three days before a general election. The attackers claimed to represent Al Qaeda in Europe.

Sir Stevens said "a number" of attacks had been thwarted in London and "hundreds" of terrorist suspects were being processed in British courts, according to extracts on the BBC website. He would not give any details.

Like other senior public figures here, he reiterated that Britain was a prime target for radicals. "The risk of an attack to London has not changed. An attack is still inevitable."

Only last month, the head of Britain's security service MI5, Eliza Manningham Buller, also warned: "There might be major attacks like Madrid earlier this year." Britain is considered a target for radicals due to its support of President George W. Bush, particularly in Iraq.

Although there has been no attack on UK soil, the threat was illustrated a year ago with a suicide bombing at a consulate in Turkey that killed 17 people including the consul general.

Critics, however, accuse both UK and US authorities of scare-mongering, in part to bolster their power. Britain has arrested more than 600 terrorism suspects since the Sept 11, 2001, attacks on the United States - but has charged fewer than 100 and convicted only 15.

Also on Thursday, Britain and the United States announced a new agreement to develop counter-terrorism technology together. The accord, signed by Britain's Home Secretary David Blunkett and US Homeland Security Deputy Secretary James Loy, will allow greater information exchange on security issues. -Reuters