Air safety is said to be unaffected by the computer failure

The situation was returning to normal as evening approached, but some arrivals and departures were still disrupted.

The West Drayton control centre is now fully operational and the cause of the fault was being investigated.

National Air Traffic Services said flights had been grounded so that controllers could prioritise on planes in the air - but safety had been unaffected.

A spokesman for Cardiff International Airport said flights had been held up by as much as two hours.

Flights have also restarted at Bristol International Airport, and passengers have been advised to turn up as normal.

At Manchester, flights were grounded between 0610BST and 0700BST, and there was a knock-on effect throughout the day.

The affected computer systems were not those that handle the separation of aircraft in the air.

The Transport Secretary Alistair Darling had warned of "a lot of disruption" and said the problems followed an overnight computer upgrade.