British Airways cabin crew launched a fresh wave of strikes today, digging in for a series of walkouts as the airline cancelled a number of flights disrupting travel for passengers.
Members of Unite mounted picket lines at Heathrow Airport at the start of a five-day stoppage after hopes of resolving their bitter row with the company collapsed.
The union said the action was "strongly supported" and clashed with BA over the effect of the strike on flights.
BA said it operated more than 60% of its long-haul programme and more than 50% of short-haul flights from Heathrow, while services from Gatwick and London City ran as normal.
More than 60,000 customers will travel with BA every day this week despite the industrial action, the airline said.
BA had to axe three of its Heathrow to New York flights today and also cancelled one of its two Heathrow-Miami services.
Other cancellations included five of the nine Heathrow to Milan services, four Heathrow-Paris flights and two Heathrow-Madrid flights.
Domestic service cancellations included eight Heathrow to Manchester flights and seven Manchester to Heathrow services.
Meanwhile, leaders of BA pilots described as "nonsense" suggestions from the British Airlines Stewards and Stewardesses Association (Bassa) that a deal could not be done because they objected to travel perks being restored to staff who went on strike in March.
Jim McAuslan, general secretary of the British Airline Pilots' Association (Balpa), said: "It is nonsense to claim that pilots are doing anything to prevent a settlement.
"Indeed, to avoid making a bad situation worse, we have stayed neutral throughout this dispute despite the huge damage to the company's reputation and the very real risk that it poses for the future of all employees. We have encouraged both sides to reach agreement and helped initiate the new coalition Government's attempt to bring the two sides together.
"Such claims by some cabin crew members are a deliberate attempt to drive a wedge between the two communities - cabin crew and flight crew - at an already difficult time.
"The claim also seeks to shift the blame for the lack of resolution to this dispute on to pilots' shoulders and away from where it should be. It is regrettable that the Bassa branch in Unite should resort to such tactics."
Striking workers gathered at a football ground near Heathrow's perimeter fence, creating a party atmosphere, although stressing they had nothing to celebrate.
They wore badges reading "Brutish Airways" and many waved Unite flags and chanted slogans attacking BA chief executive Willie Walsh.
As they boarded buses to transport them to picket lines some did not want to speak to media, saying they were in fear of losing their jobs after hearing that others had already been sacked.
Three female crew members, with more than 80 years' experience with BA between them, said they were not typical pickets - but felt the principle behind the strike was too important to ignore.
One of them, wearing pearls and waving a placard, said: "We remain very positive. We have had a fantastic reaction from people driving past. We've even been bought coffee and doughnuts.
"My message to passengers is this - turn to Willie Walsh. He had a no-cost option given to him yesterday, all he had to do was restore something."
BA said its operations around the world got off to a good start, with enough cabin crew reporting at Heathrow to operate its published schedule.
"We will fly more than 60,000 booked customers around the world every day between May 24 and May 28, despite these five days being targeted for strikes by Unite.
"Many thousands more will be able to use seats we have secured on more than 50 other airlines to reach their destination if they still wish to travel, or be rebooked on to an alternative BA flight departing within the next 355 days.
"Refunds are also available for customers whose flights have been cancelled.
"We will be operating the majority of our revised short-haul schedule at Heathrow using our own aircraft and cabin crew, but this will be supplemented by leasing up to eight aircraft with pilots and cabin crews from other UK or European airlines."
Tony Woodley, Unite's joint leader, accused Mr Walsh of wanting "regime change" in Bassa.
Mr Woodley said BA had achieved its original aim of cutting 1,700 cabin crew jobs, but had since "broadened" the dispute.
Mr Woodley said the strike would have been suspended if BA had accepted his offer to call off the action if the airline returned travel concessions to staff who took part in strikes in March.
Passengers arriving at Heathrow today questioned the reason behind the strike.
Maureen Lonergan, 66, from St Helens, Merseyside, had her flight from Manchester to London brought forward by a day ahead of her trip to Venice with husband John.
Arriving at Heathrow's Terminal Five, she said: "It has inconvenienced us. We only had one day's notice and have had to arrange to stay at a hotel in London, and pay for it ourselves.
"I think the strikers are greedy. We've heard they get paid more than other airline staff anyway."
Sam Hillier, 41, from Northampton, had been on holiday to Las Vegas and New York with friends. The group had their original flight to Heathrow changed to one that left New York three hours earlier than planned because of the strike.
She said: "We had a bit of hassle having to ring up to change things.
"I think they're really silly to strike when there's been so much disruption over the ash cloud.
"They must have lost millions already. If I was a competitor I'd be trying to grab their passengers."
David Cameron's spokesman said: "The Prime Minister wants to see as little disruption to passengers as possible.
"The best way to achieve this is for the two parties to resolve the situation as soon as possible."
Unite said tonight its offer to suspend the strike if BA fully restored travel concessions still stood.
The union has announced two further five-day strikes after this week's walkout ends.