As the UK tries to come to terms with the devastating Istanbul bombings, British security chiefs have warned of worse attacks and have said even the British mainland is not safe.
London Metropolitan Police Commissioner Sir John Stevens has confirmed that a number of attacks on London had been foiled in the past two years, thanks to the police and security services MI5 and MI6.
Also see: UK interests in Istanbul hit; 27 dead
Sir John, who was being interviewed on a radio programme, appealed to the public to "work with us and support us."
The Istanbul bomb attacks, which targeted the British consulate and the local headquarters of the HSBC Bank, left 27 and dead and 450 injured.
Among the dead were UK Consul General Roger Short and his personal assistant Lisa Hallworth.
The twin strikes came after a message from a terrorist group warned that the UK was in its sights because of London's support to the US in the war against Iraq.
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"Everyone should know that what is coming will be even worse," said the message sent by the Brigades of Abu Hafz al Masri, which also claimed responsibility for an earlier attack on two synagogues in Istanbul.
"We tell the criminal Bush and his lackeys, both Arab and foreign, especially Britain, Italy, Australia and Japan, that the cars of death will not be limited to Baghdad."
The group is named after Hafz al Masri, who was killed in US bombings in Afghanistan two years ago, and is closely associated with the Al Qaeda network.
In London, both Prime Minister Tony Blair and President George Bush have vowed they will not back down in their war against terrorism.
On Thursday, Blair told a press conference in London, "There must be no holding back, no compromise, no hesitation in confronting this menace, in attacking it wherever and whenever we can and in defeating it utterly.
"I can assure you of one thing - when something like this happens, our response is not to flinch or give way or concede an inch. We stand absolutely firm until this job is done in Iraq, done elsewhere in the world."
Bush said, "These terrorists hope to intimidate, they hope to demoralise free nations. they are not going to succeed. We will finish the job we have begun."
