The travel plans of thousands of air passengers were thrown into chaos tonight when a computer fault at the UK's main air traffic control centre led to serious flight disruptions.

The problem started just before 4pm today when a fault occurred at one of the systems at Swanwick Air Traffic Control Centre in Hampshire.

This led air traffic control company NATS to restrict the number of planes entering UK airspace as well as those taking off from major UK airports.

There were reports that all flights at Luton Airport were suspended. Flights at Heathrow Airport were also disrupted.

mf NATS said: ''Engineers are investigating the cause of the fault and working to restore the system as soon as possible.''

The company said the restrictions on take-offs and landings were to maintain safety while controllers operated with manual systems at reduced capacity.

The company added that Scottish airspace and Manchester area airspace were working normally and that only sectors controlled from the London area control centre were affected.

There have been a series of computer problems which have affected air traffic control on and off over recent years.

The opening of the Swanwick centre was delayed for some months due to NATS needing to iron out computer problems and there have also been problems which have caused delays at London airports when systems have failed at the West Drayton centre near Heathrow.

At London's Heathrow airport flights were taking off every five minutes, less than the airport's usual rate. A spokeswoman said: ''The operation is slowing down.''

At Stansted airport arrivals were unaffected but departures were subject to delay.

''Flights are departing but at a reduced level,'' said a spokesman.

A spokeswoman for Luton Airport said that cancellations were possible but ''this is not a blanket cancellation of all flights.

''We are suffering delays due to the restrictions placed on flights by NATS.''

Gatwick Airport was warning passengers that delays were possible and a number of arriving flights were delayed.

A spokesman for airport operator BAA - which runs Heathrow, Gatwick, Stansted, Glasgow, Edinburgh, Aberdeen and Southampton airports said: ''Due to an interruption to the air traffic control service, run by NATS at Swanwick, flights from many UK airports are subject to some delays and cancellations.

''Aircraft continue to land and depart, however the process is slower than normal, which means that inevitably, some flights will be delayed and some will be cancelled.

''We are working hard with the airlines to minimise disruption and restore the operation as quickly as possible.

''Passengers are advised to contact their airline or see www.baa.com before travelling to the airport''.