THE centre of London will be flooded with 14,000 police officers for President Bush’s three-day visit which begins tonight, in the biggest and most expensive security operation seen in Britain.

Security chiefs are even considering shutting down all mobile phone signals near the President every time he leaves Buckingham Palace in case terrorists try to use a mobile to detonate a bomb.

Britain was put on the highest terror alert since the September 11 attacks last week after a terrorist suspect told police that Algerian supporters of al-Qaeda were planning an attack soon.

The suspect, who is in a top-security prison, says that there are between 15 and 20 people ready to launch a deadly attack, although it would not be directly linked to the President’s visit.

Special Branch officers have also warned the American Secret Service that a “mentally deranged lone fanatic with a fixation for George Bush” may be at large in the capital.

In spite of such concerns Tony Blair again defiantly stood by his decision to invite Mr Bush, saying that recent attacks proved that Britain and the US were involved in “a worldwide struggle against fanatical and extremist groups”. He said: “Now is not the time to waver. Now is the time to see it through.”

But the Mayor of London, Ken Livingstone, branded Mr Bush as “the greatest threat to life on this planet” whose policies will “doom us to extinction”. The mayor also said that he did not recognise Mr Bush as a lawful president and he condemned America’s rapacious capitalist agenda.

The police response to the President’s visit, which will include the deployment of the vast majority of the 2,000 officers authorised to carry firearms, was expanded after a ruling yesterday that the 100,000 protesters expected in London on Thursday will be allowed to march down Whitehall, raising fears that many will try to reach the President’s motorcade.

The operation, which involves half of Scotland Yard’s entire force, will push the likely cost to more than £10 million and has raised fears of a crimewave in suburban London while officers are so obviously deployed elsewhere.

Scotland Yard said that it would not draft in officers from neighbouring forces but that it would use British Transport Police, the Royal Parks Constabulary and officers from the City of London force.

Senior officers insisted last night that the reinforcements would not give criminals a free run in the rest of the capital, although they admitted that “resources will be stretched”.

The White House has intensified its own security plans. There will be 250 armed US agents travelling as part of Mr Bush’s entourage, although Scotland Yard has told them that it is in overall control.

But as the final stages of the ring of steel were being put in place last night there was embarrassment when a woman eluded police to scale the main gates of Buckingham Palace to protest against the visit.

Lindis Percy, 61, a nurse from Yorkshire and veteran peace protester, has been arrested on several previous occasions for campaigning at nuclear weapons sites and US military bases around Britain.

Firemen on ladders tried to talk Ms Percy down while police tried to calm fears of White House officials that protesters could repeat her feat while Mr Bush is in residence. She later came down and was taken into custody.

The main concern for police masterminding the security operation is that Thursday’s demonstration is now expected to draw well over 100,000 protesters into the capital, with militant anarchist groups are threatening violence.

To try to avoid a confrontation with demonstrators Scotland Yard last night agreed that they could march down Whitehall. This will take them past Parliament and Downing Street despite the demands of the White House that an exclusion zone should be enforced. Marchers will not be allowed anywhere near Mr Bush.

Deputy Assistant Commissioner Andy Trotter said: “We are on a very high level of alert at the moment. We obviously have the visit of the President coinciding with that and we’ve got to make sure that London is kept safe and the visit goes well.”

Armed police yesterday kept watch at ports, railway stations and airports for known troublemakers. There will be “rolling road-blocks” put in place whenever Mr Bush’s motorcade takes to the streets and US military helicopter gunships will patrol over Central London.

After he touches down at Heathrow for a brief welcome from the Prince of Wales, Mr Bush will be flown in his own helicopter to Buckingham Palace where he and his wife, Laura, will stay for the next three nights. He will make fewer public appearances than any other visiting head of state to reduce the risk of a terrorist attack, say his aides, not to spare his embarrassment over anti-war protesters.

He will make his big speech in the Banqueting House, Whitehall, tomorrow, and will also hold talks with Mr Blair tomorrow, and give a joint press conference with the Prime Minister.

On Friday morning, when he flies to the North East as a guest of Mr Blair, there will be a further 1,300 police on duty in Sedgefield for his day trip. Extra officers are being brought in from neighbouring forces and all leave has been cancelled.

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