Anti-terror police are relying on public help to stop an attack in London, the Met's chief said today.

Met Commissioner Sir John Stevens today spoke of steps being taken to prevent an attack in London, in the wake of widespread alarm after last week's bombings in Madrid.

Sir John said London's Tube and rail network remained an obvious target.

"But we are also talking about London in general. This is a general message for Londoners to remain alert," he said.

While Britain had highly trained anti-terror police, Sir John said they were relying on information and assistance from the general public.

Put your views in our survey of how London's taking the terrorism threat

"We cannot defeat terrorism alone," he said.

Sir John agreed with Government suggestions that a terror attack was inevitable in London.

Speaking at a press conference with mayor Ken Livingstone, Sir John said police were working three times harder than ever' to prevent an attack.

About 500 people had been arrested and 90 of them were due to come before court in the next year.

"Take my word for it, we have foiled a major event," he said.

"A major attack in London will not be easy to handle, none of them are, but we do have experience."

Sir John compared the work of anti-terror police to a game of chess, where authorities analyse the latest moves of their opponents to take action before an attack.

Mr Livingstone joined with Sir John in encouraging people to carry on their normal lives.

The mayor said London was the safest world city' and terrorists had shown they would attack anywhere in the world, from Madrid to Bali.

Local London terror survey

Please take a few moments to fill in this survey about Londoners' attitudes towards the threat of terrorism.

Results will be posted on the site tomorrow (Wednesday)

Do you agree or disagree with the following statements about the threat of terrorism to London?

1) London is safer from terror attack since the war on Iraq.
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2) The Metropolitan Police provides an effective guard against terrorism.
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3) The Government should take stronger measures to fight the threat of terrorism.
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4) Spain is right to pull its troops out of Iraq and Britain should do the same.
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5) Most Londoners do not let fear of terrorist attack affect the way they live.
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5) Londoners lives were more at risk during the IRA bombing campaigns.
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