More British Airways flights were cancelled today as staff shortages and technical problems continued to blight thousands of passengers' journeys.
A further 10 flights, to short-haul destinations in domestic and European locations, were cancelled this morning.
BA, which would normally expect to carry around 100,000 passengers throughout the day, said there would be further minor delays to short-haul journeys.
A company spokesman said this morning: "I cannot rule out more cancellations. It all depends on how operations go.
"Passengers should consult our website. We urge passengers to take a look at that."
The problems began yesterday afternoon after the airline cancelled three long-haul flights to the United States over technical problems with the aircraft.
The disruption worsened BA's current staff shortages and led to the cancellation of another 22 flights - most of which were short-haul - and others being delayed.
Up to 5,000 passengers are thought to have been affected by the disruption, which comes at one of the busiest times of the year for the airline industry.
Some were accommodated on later flights, some were provided with overnight hotel accommodation and seats on flights today, while others simply had to rebook.
An earlier statement issued by BA said: "We apologise sincerely to those customers affected by the disruption to flights at Heathrow Airport yesterday.
"Due to a number of operational reasons we have cancelled 25 flights and some services have been delayed."
It added: "August is the busiest period of the year for British Airways and services at Heathrow are stretched.
"We have also had some technical problems with our aircraft and these combined has resulted in the cancellations.
"Our staff are working extremely hard to ensure operations return to normal."
The US-bound flights cancelled due to technical problems were those to Philadelphia, Chicago and New York.
Among the short-haul flights that were cancelled were those to Edinburgh, Munich and Aberdeen.
Only last weekend, a planned strike by BA workers for the August Bank Holiday weekend was called off.
The strike had threatened to cause travel chaos to tens of thousands of holidaymakers.
However, unions representing baggage handlers and check-in staff at airports, including Heathrow and Gatwick, agreed a pay deal with managers to head off the 24- hour walkout.
BA has agreed an 8.5% pay increase over three years as well as £1,000 payable in three lump sum payments between now and September 2006.
A spokesman for British Airways at the airport said today that the airline's Heathrow operation was around 120 staff short of full strength.
He said: "That is mainly due to sickness, and also the fact that we had more people leaving at the beginning of the summer than what we expected.
"We are recruiting, but the main problem with recruiting is not only training but also the security aspect."
Twenty-one flights have been cancelled today - 11 outgoing and 10 incoming - affecting an estimated 2,500 people, on top of those cancelled yesterday.
Destinations affected today include Munich, Berlin, Frankfurt, Zurich, Stuttgart, Nice, Glasgow, Aberdeen, Madrid, Helsinki and Stockholm.
One of those hoping to travel to Madrid who was hit by the cancellations was Paul McGowan, 27, an Australian living in Manchester.
He said: "We were meant to fly at 10 o'clock and our flight has been cancelled. We were told possibly there might be a flight at 11.30 or 12.30. It's a bit of a concern as we have a connecting flight to Valencia, that's at about 4.30pm Madrid time.
"We just went up to the desk and they said 'You are in the right line, but it has been cancelled'."
Mr McGowan added that he had been told to queue up at the ticket sales desk to find a replacement flight but said: "It's a world-renowned company. They should have the infrastructure in place to ensure they have adequate staff."
His fellow traveller, David Chapman, 23, from London, said: "It's an inconvenience, it sucks."
- More about:
- Air Transport