A day of airport chaos signalled the start of what appears to be a summer of travel misery.

Soaring petrol prices and the decision by Gatwick and Heathrow baggage handlers to strike were just the start.

At 6am yesterday calamity struck when an air traffic control computer system crashed.

Planes across the UK were grounded and although the fault was fixed an hour later, flights were delayed all day. Passengers had to wait in sweltering departure lounges for hours.

National Air Traffic Services (Nats), the privatised body in charge, apologised to the thousands of people affected and promised the system would not shut down again.

Many were sceptical. After all, this was merely the latest embarrassing fiasco for air traffic control in recent years.

While flights yesterday were delayed for several hours, computer problems meant Nats' showpiece £623 million HQ was six years late when it finally opened in January 2002.

Yet 30-year-old systems are still being used at the West Drayton base, near Heathrow, which was meant to be replaced by the newer facility in Swanwick, near Southampton.

And although yesterday's chaos was initially blamed on systems at Swanwick, it soon emerged the fault originated at the older offices during tests for a computer upgrade.

West Drayton controls all air traffic in and out of London's airports and also houses the computer providing information to controllers at Swanwick, who look after flights for the rest of England and Wales.

The 600 staff at West Drayton are due to transfer to Swanwick in 2007, though computer experts warned that date could be put back.

Yesterday's problem centred on West Drayton's flight data processing system, which is based on Jovial software from the mid-Seventies.

Staff at West Drayton had to write down flight details and relay them to Swanwick.

Tony Collins, executive director of Computer Weekly magazine, said: "Even some people in the computer industry have never heard of this program as it goes back so far.

"Although the hardware is new, the software is old. They have been upgrading parts of the software but it is very much a patched-up system and that doesn't help."

Nats chief executive Richard Everitt admitted: "The system has to be upgraded. We are doing a major upgrade later in the year. Morale is not low at the centre.

"I would like to apologise to all passengers and tell them we are doing our best to minimise disruption to them."

The apologies, whether from Nats or harried airport staff yesterday, provided small comfort for people facing excruciating waits or cancelled services.

Flights were grounded at Gatwick between 6.30am and 6.50am after staff there were told of a problem at 6.15am.

British Airways cancelled six flights, to Amsterdam, Edinburgh, Luxembourg, Munich, Turin and Pisa.

Budget airline easyJet scrapped four, to Amsterdam, Edinburgh, Inverness and Nice.

Airport bosses estimated 48,500 were travelling through the airport yesterday.

A BAA Gatwick spokeswoman said: "We've been slowly getting back on track, though people will probably still face delays of one or two hours."

During the afternoon, people lolled in the departure lounge, with many taking the opportunity to catch up on a bit of rest.

Parents rushed to WH Smith to stock up on colouring books, sweets and soft drinks to keep their youngsters occupied as more delays flashed up on the overhead screens.

Mother-of-three Anne-Marie Turnell had three youngsters under seven to keep entertained after hearing their flight to Spain would be delayed.

Mrs Turnell, 38, arrived at Gatwick with husband Stephen, mother-in-law Eileen Turnell, sons Jack, six, and Alfie, four, and three-year-old daughter Abbie at 11.30am yesterday.

Check-in staff told her the 1.35pm flight would not be leaving until 5.05pm.

Mrs Turnell, from Essex, said: "We saw it on the news before we set off to we called up to check everything was all right.

"With three kids you don't want to be left stranded at an airport.

"We were told the delays shouldn't affect Spanish flights so we drove down here, only to be told our flight would be late."

Mr Turnell, a security guard at the Bank of England, was handed £3 refreshment vouchers for each person in compensation.

Mrs Turnell said: "We've bought the kids some books and had lunch and now we're just chilling. There's nothing we can do about it."

Kelly Wilderspin, a signmaker from Southend, Essex, said he was angry at the delays and planned to sleep until his flight to Almeria.

His wife Diane opted to play cards with their daughter Catherine, seven, to pass the time.

Mrs Wilderspin said: "We're just going to take it as it comes, although it is very inconvenient and upsetting to start a holiday like this.

"We only found out after we had checked in so it was too late to do anything about it."

Nick Saunders, 30, had travelled from London to be told his BA flight to Pisa would be delayed by three-and-a-half hours.

He was meant to take off at 2.25pm but was settling down for the wait until 6pm.

Mr Saunders said: "I checked the web site and it made no mention of the flight being delayed. It's annoying. The whole thing seems so disorganised."

By 2pm about three-quarters of flights on the departures board were delayed, some into the evening.

Passengers heading for the sunnier climes of Toulon in southern France were meant to take off with BA at 4.10pm.

According to the departures board, there was no time set for the flight, with the only advice being "next info 19.27".

The scene in arrivals was similar. Many flights were delayed and others, such as the 1pm American Airlines flight from Edinburgh, cancelled.

Staff at the information desk in the South Terminal said domestic flights were worst-affected.

Due to restricted airspace, international flights had been given preference.

Staff said the worst disruption had been between 8am and 10am and flights were expected to be back to normal by yesterday evening.

Transport Secretary Alistair Darling insisted Britain's air traffic control was "very good" compared with other countries.

He said: "If you want to know what is wrong with transport in this country it is that over decades, successive governments did not spend enough on the infrastructure and air traffic control is no different.

"We are putting the money in. It is making a difference."

Nats had wanted to move into the Swanwick base in 1996 but had to repeatedly postpone the opening because of computer software problems.

When it finally went operational on January 27, 2002, Mr Everitt said:

"Britain can now boast the most technically advanced air traffic control centre in the world."

But some flights were delayed for a few days after the grand opening and computer problems at West Drayton continued to cause serious hold-ups in July 2000 and again in 2002.

The last time Gatwick suffered as badly as yesterday was in May 2002, when computer glitches at Swanwick caused 30 flight cancellations and six-hour delays.

The breakdown was the third in two months. Three months later it emerged staff shortages at Swanwick meant the centre was handling fewer planes than the West Drayton base it was replacing.

Even if air traffic control runs smoothly for the rest of the summer, passengers at Gatwick face further disruption.

Transatlantic travellers could have to queue for almost five hours to check in because of new US security measures.

American authorities will require detailed information such as passengers' visa details.

Strikes by baggage-handlers at both Gatwick and Heathrow are also imminent, although dates have not yet been announced.