Media playback is unsupported on your device Media caption Some airlines are cancelling short-haul flights but trying to only delay long-haul services

A telephone glitch that caused hundreds of flights to be delayed has now been resolved, but disruption is continuing.

Thousands of passengers faced cancellations and long waits after the National Air Traffic Service (Nats) internal phone system broke down.

Affected airports included Heathrow, Gatwick, Stansted, Cardiff and Glasgow.

Nats announced at 1930 GMT that the problem had been fixed, but some airports said delays could continue into Sunday.

Analysis A fault with a complicated internal telephone system brought delays and cancellations for thousands of travellers today. The controllers at the air traffic control centre in Swanwick, Hampshire, use it to swap important data about aircraft, it's vital to help them perform their job even though many of them are sitting in the same room. That system failed to work this morning as they tried to switch from the quieter, night time mode, to the busier daytime mode. It meant they couldn't open all the work stations needed to cope with a normal Saturday, so they've been running a reduced service ever since. Instead of 3,500 flights, they've only been able to process 2,800 or so. Nats tell me they've never had this problem before, and that it's totally different to a computer glitch that caused some delays last summer. Even so airline Ryanair isn't happy at having to cancel and disrupt so many flights. In a statement it acknowledges that problems occur, but asks the question "where is the contingency?" It's the airlines that normally pick up the bill for compensation.

A passenger who said he had been waiting five hours at London's Gatwick airport earlier told the BBC that people had been "crying, distraught and angry".

"One passenger has missed their sister's wedding," Tom Flatman, from Brighton, said.

'Severely delayed'

By 16:00 GMT Nats said it had handled 2,576 flights compared with 2,905 at the same time last week.

Ryanair said 300 of its flights were delayed on Saturday with 12 cancelled, and called on the Civil Aviation Authority (CAA) to act.

"While we acknowledge problems can occur, where is the contingency?" it said in a statement.

Heathrow had cancelled 228 flights by 18:55 GMT, a spokeswoman said, adding that there was now an average one-hour delay for departures.

By Saturday evening Gatwick airport said it was "returning to normal operations". A spokeswoman said it was "not expecting serious disruption" on Sunday.

Delays at Stansted averaged two to four hours, a spokeswoman for the airport said, adding that schedules were expected to return to normal on Sunday but warning there could be "minor delays".

No Easyjet flights have yet been cancelled but many were subject to delays.

It is not the first time that the state-of-the-art facility has hit the headlines" Swanwick 'plagued by problems'

Eurocontrol - which manages European air safety - said around 1,300 flights, or 8% of all air traffic on the continent, had been "severely delayed".

Meanwhile, elsewhere:

A spokesman said Manchester Airport had been "only minimally affected" and operations were now back now back to normal

Leeds Bradford, Doncaster Robin Hood and Newcastle airports all reported minor delays, with flights to London worst affected

Belfast International Airport and Dublin Airport reported a number of cancellations

A spokeswoman for Birmingham Airport said around 60 flights were affected, the majority were delayed by under an hour

Nats said the problem at its Swanwick centre, in Hampshire, arose in the early hours of Saturday morning when the night-time operation failed to properly switch over to the daytime system.

"The problem that arose this morning with the ground communications system in the area control operations room at Nats Swanwick has now been resolved and operations are returning to normal," a spokesman said.

Biggest in Europe

The software failure happened when the 23 controllers working overnight were due to hand over to the 125 on the day shift at around 06:00 GMT.

"To be clear, this is a very complex and sophisticated system with more than a million lines of software," the spokesman added.

"This is not simply internal telephones, it is the system that controllers use to speak to other [air traffic control] agencies both in the UK and Europe and is the biggest system of its kind in Europe."

Image caption Passengers at Heathrow Terminal 5 queued as British Airways warned of delays

Image caption Some passengers at Gatwick Airport resorted to sleeping while they wait

Image caption Nats said how quickly things would return to normal depended on individual airlines' schedules

Image caption At Heathrow's Terminal 3 the queues stretched outside the building

Compensation for delayed flights In certain circumstances EU travellers can claim back up to €600 for delayed flights

Claims can be made for flights that were delayed up to six years ago

Airlines should always provide refreshments after a two-hour delay and accommodation if it the flight is delayed overnight

The BBC's transport correspondent Richard Westcott said it was a totally different issue to a software problem that hit the control centre in summer.

Nats head of operations Juliet Kennedy told the BBC: "We want to apologise to people. We are very aware of how much inconvenience this has caused people."

'Shambolic'

The CAA advised customers affected to contact the airline concerned to discuss their case.

It pointed out that customers could claim assistance from their airline if they were delayed for several hours, including being given food and drink, usually in vouchers.

Live updates For live travel updates follow BBC Travel News UK which covers delays across the country BBC Travel News Air

At Stansted, Alena Kontza was stuck on a Ryanair plane that had been delayed for three hours. She told the BBC passengers had been given "absolutely no information" and "it's been nothing less than shambolic".

"People are really aggravated, children are crying, people want to leave, people want to change to different planes, it's an absolute nightmare," she said.

Media playback is unsupported on your device Media caption National Air Traffic Systems: "We are not able to meet the demands"

A spokeswoman for British Airways said: "We are organising hotels for customers when appropriate. In addition, customers on cancelled services of course have the opportunity to claim a refund or rebook."

Independent aviation analyst Chris Yates said it had been a "trying and a very tough day", adding: "There's going to be a lot of hard questions asked of Nats over the coming days.

"In the meantime we have to get back to a normal service."