Hundreds of air passengers were left stranded after an air-traffic control system crashed.

Seven flights from Gatwick were cancelled following the fault yesterday morning.

Passengers to Marseille, Prague, Venice, Amsterdam, Pisa and Rome had to find alternative ways of getting abroad.

Other services were delayed by more than an hour.

The computer failure occurred at the National Air Traffic Services (NATS) centre at West Drayton in west London at 9.30am.

Gatwick was still getting back to normal at 3.30pm.

The seven cancelled flights were operated by British Airways, which earlier this month had to axe hundreds of flights because of a continuing catering dispute.

A spokeswoman for the airline said it did what it could yesterday to help passengers turning up for cancelled flights.

She said: "We tried to re-book passengers on other flights or we offered them a refund. We do have more than one service to those destinations."

A Gatwick spokeswoman said: "During the period, only departures were affected.

In-bound arrivals continued as normal.

"There have been knock-on effects. Some flights were cancelled and there have been some delays. Some flights were affected by about an hour."

NATS said its flight data processing system was restored to full operations by 9.50am.

A spokesman said: "The system at West Drayton which provides flight progress information for controllers failed at 9.30am. The cause of the failure is still being investigated.

"The system was up and running within 20 minutes but we had to delay some outbound flights from UK airports while the system was down."

He said the average delay by the end of the day was expected to be about ten minutes.

Ian Hall, NATS' director of operations, said: "We sincerely apologise to those who have been inconvenienced. We did everything we could to restore the full air traffic control service as quickly as possible and minimise the delays and impact on the day's schedules."

A serious computer problem at West Drayton in the summer of 2000 led to severe delays to UK flights.