Gatwick was among the airports affected by the computer failure

Major delays were caused at airports including Gatwick, Heathrow, Manchester, Glasgow and Inverness.

An initial suspension of departing flights ended when Air Traffic Control switched to a manual back-up system.

At Heathrow, the UK's busiest airport, there were no departures at all between 0630 and 0704 BST.

Improvement

A spokeswoman for the British Airports Authority (BAA) said Heathrow had returned to full operations by late morning and was "well on the road to recovery" from the disruption.

"We are experiencing delays across some flights of up to 90 minutes, which we expect to reduce throughout the day," she said.

Passengers should contact their airline for information on the status of their flight, she added.

At Gatwick, there had been no flights for 20 minutes between 0630 and 0650, an airport spokeswoman said.

There are a significant number of delays and we ask for the patience and understanding of the public BAA spokesman in Scotland

"There have been delays of one to two hours this morning, with the longest being three hours," she said.

By early afternoon, there was still a backlog of delayed flights which were experiencing an average delay of between one and two hours, the BAA said.

Disruption also affected passengers travelling from Stansted, but aircraft continued to land despite this, an airport spokesman said.

"There was a half-hour suspension of departures until the manual back-up system was in operation but most of the inbound traffic continued with minimal disruption," he said.

Things were improving at Manchester airport, where the list of delayed flights was quickly being cleared, a spokesman said.

"Outbound flights were grounded between 0610 and 0655, affecting 30 aircraft, but arrivals continued to land as normal during that time," he said.

"Airlines are saying that passengers are advised to turn up as normal."

CANCELLATIONS Heathrow: 30 arrivals and 30 departures cancelled Gatwick: 10 cancellations Stansted: 8 arrivals and 7 departures cancelled Glasgow: 9 arrivals and 12 departures cancelled Edinburgh: 9 cancellations Source: BAA

At Bristol International Airport, flights were grounded for approximately one hour from around 0630, a spokeswoman said.

A spokesman for the BAA in Scotland said things were getting "slowly back to normal".

"There are a significant number of delays and we ask for the patience and understanding of the public," he told BBC News Online.

"We are hopeful of clearing the backlog as soon as possible but we can't put a time on it."

Services were back to normal by mid-morning at Southampton, with some minimal delays expected, while Easyjet cancelled a number of flights from Luton, where delays were expected throughout the day .

At Birmingham airport, early-morning delays occurred but operations were expected to return to normal by the end of the day.