Thousands of passengers face delays and cancellations - to allow President Bush's Air Force One jet to land at Heathrow

The U.S. President is refusing to fly in to a military base and has demanded that he land at the world's busiest airport.

Security concerns mean arrivals of commercial flights will be almost halved for an hour before the fleet of planes, including Air Force One, touches down on Sunday.

President George Bush and his wife Laura will land at Heathrow on Air Force One on Sunday. But their visit is set to cause chaos at the world's busiest airport

Industry experts predict the knock- on effects will last for up to six hours.

Departures will also be hit because planes arriving late will not be able to turn around quickly enough to meet take-off times.

The entire process will be repeated when the President leaves on Monday.

Last night Heathrow sources were predicting chaos at the airport, whose image is still recovering from the Terminal Five fiasco.

'For some inexplicable reason Bush wants to fly in to Heathrow,' a source told the Mail.

'It is going to cause massive delays and possibly even some cancellations. It is ridiculous and the arrangements are total overkill.'

The fleet includes the 747s Air Force One and Two, a smaller 757 and four helicopters.

Yesterday, there were some minor delays after air space over Heathrow was cleared for two hours to allow a military cargo plane carrying the President's armoured cars to land at nearby RAF Northolt.

Today there is also likely to be some disruption when the four helicopters land and sit on the tarmac for an hour as part of a dress rehearsal.

According to airport sources, an hour before Mr Bush arrives the number of flights allowed to land will be cut from 42 to 24 an hour. Once he has touched down the restrictions will be gradually lifted.

There is even a suggestion that a runway will have to be closed before touch-down so that it can be inspected by security sources.

Similar limits will be in place again on Monday when Mr Bush leaves. 'We think the knock- on effects will last for at least six hours,' an insider said.

'Although it hits arrivals first, departures later in the day will also be affected because airlines won't be able to turn round planes in time and crews will need sufficient rest breaks. If a plane doesn't come in on time then it doesn't go out on time.

'This is basically going to effect everyone flying in or out of Heathrow on Sunday and Monday and a fair few people on Friday, too.'

Airlines had only been told on Wednesday about the plans and it was claimed last night that the Department for Transport had also been kept in the dark as all arrangements had gone through the Foreign Office.

Mr Bush is visiting London as part of his farewell tour before he leaves the White House next January.

Defence officials believe the president and his entourage could have landed at RAF Brize Norton in Oxfordshire or the vast U.S. airbase at Lakenheath in Suffolk.

'No one knows why on Earth he wants to come to Heathrow,' one said. 'It's not as if he is going to stay and have a look around.'