AN unprecedented security operation will surround George Bush's visit to the North-East this week as police and secret service leave nothing to chance.

The US President, who arrives in Britain tonight, is to visit Tony Blair's Sedgefield constituency in County Durham on Friday.

Last night, police revealed that the operation to keep him safe will cost the region more than £1m for his fleeting visit.

The Durham force is talking to the Home Office to recoup the cost after it was feared council tax payers would help foot the bill.

Mr Bush will have lunch with the Prime Minister and a group of his constituents, but details of the North-East itinerary are still a closely-guarded secret.

All day yesterday, US planes were arriving at Teesside Airport packed with security equipment.

Four US helicopters held a dry run for a possible presidential arrival at the Prime Minister's constituency home at Trimdon Colliery.

Two Sikorsky aircraft from the US navy's elite Black Stallion combat support squadron landed on a field close to Mr Blair's house.

They were followed by two further helicopters bearing US Government livery as part of a dummy run.

Police used cameras to check drains before sealing them shut, fitted anti-tamper devices to external gas meters and patrolled the grounds of Mr Blair's home with sub-machine guns.

Meanwhile, Durham Police have cancelled all leave as the finishing touches are put to the operation, which will involve 1,300 officers - some drafted in from neighbouring forces.

The force has overall control of the North-East leg of Bush's state visit to Britain, which will attract hundreds of protestors from across the region.

In London, the Metropolitan Police has decided to increase from 5,000 to 14,000 the number of officers on duty for security reasons, but denied the force was planning to clamp down on protests at the behest of the US.

Police remained "very concerned" about the general threat of an al Qaida attack on the capital and is on a high state of alert.

Durham Assistant Chief Constable Gary Barnett said the force was also liaising with the Metropolitan Police to ensure continuity.

Assistant Chief Constable Barnett said that while there was no specific threat in relation to the visit, there would be a heavy police presence on all proposed routes and around the sites to be visited.

"We have no indication at this stage of the size and scale of any marches or protests that might be planned in County Durham," he said. "However, while we are mounting an operation to cover a wide range of contingencies, we are looking to balance the needs of security against people's right to demonstrate peacefully."

Anti-war demonstrators said last night they were unable to predict how many people would turn out in the North-East.

Peter Smith, of Teesside Against War, said: "We would not be doing this if we did not have strong feelings about the war. We are outraged this man has been granted a state visit."

On the eve of the visit, Tony Blair said he stood by the decision to invite the US President to Britain.

Speaking at the CBI annual conference in Birmingham, he said: "This is the right moment for us to stand firm with the United States in defeating terrorism, wherever it is, and delivering us safely from what I genuinely believe to be the security threat of the 21st Century,".

Last night, a protestor was arrested after scaling the Buckingham Palace gates with a banner telling Mr Bush he was not welcome.

The woman, who climbed down from her perch after about two hours, was named by friends as veteran anti-nuclear campaigner and grandmother Lindis Percy, from Hull.

A petition bearing 100,000 signatures denouncing Mr Bush's visit was handed in to Downing Street by protestors including Vietnam War veteran Ron Kovic, whose peace campaigning inspired the film Born on the Fourth of July.

But an ICM poll for today's Guardian found a majority of voters - including more than half (51 per cent) of Labour supporters - approved of the visit.