BA flights cancelled as crew strike

British Airways was scrambling to deal with a three-day strike launched by cabin crew on Saturday, throwing the plans of tens of thousands of travellers into chaos.

BA chartered planes from rival airlines, drafted in volunteer crew from its other work force and rebooked some passengers on other services in a bid to keep as many passengers happy as possible - but it was still forced to cancel thousands of flights.

Chief Executive Willie Walsh issued a direct apology to passengers via YouTube for the walkout, the airline's first in almost 15 years, saying it was a "terrible day for BA".

The Eurostar train service between London and continental Europe and Virgin's rail services between London and Scotland were expected to be busy as passengers sought alternate routes.

BA also warned on Saturday that the disruption would likely last several days beyond the three-day strike, because of a knock-on effect on flights that would carry through to the end of a second strike planned for March 27-30.

As protesters were readying picket lines Saturday outside London's Heathrow international airport, analysts estimated BA has already lost more than STG25 million ($A41.41 million) because of cancelled tickets and contingency costs.

The two planned strikes combined could cost the airline more than the STG63 million ($A104.36 million) that Walsh is trying to save through the disputed changes to workers' pay and conditions.

The Unite union has gathered some support from unions in the United States, Germany and Spain for its action, but they have so far stopped short of pledges for coordinated activity that would disrupt BA's ability to refuel and service the planes it is operating over the walkout.

Aside from hurting BA financially, the strike is also an unwelcome event for Britain's governing Labour Party before national elections expected before June.

Prime Minister Gordon Brown irritated Unite, a major political donor, by calling the union "deplorable," and as late as Friday evening was urging it to call off the strike.

Britain faces even more possible travel chaos in the run-up to the April 2-5 Easter break, as railway signal workers voted last week to join rail maintenance workers in a strike. The Rail Maritime and Transport union has not called dates for the walkout, but refused to rule out the long Easter weekend.

And over this weekend, engineering works on the London Underground were forcing closures between central London and Heathrow, though the Heathrow Express train service was operating as normal.

"As the country struggles out of the recession, the last thing we need is the unions holding the country to ransom," said Theresa Villiers, the opposition Conservative Party's transport spokeswoman.

BA said it would handle as many as 49,000 passengers on both Saturday and Sunday. That compares with the average 75,000 for a normal weekend day in March.

At its Heathrow base, more than 60 per cent of long-haul flights will operate, but only 30 per cent of short-haul. At Gatwick, all long-haul flights and more than half short-haul flights will run as normal.