Talks aimed at averting strikes by British Airways cabin crew collapsed today and the action will go ahead from midnight.
Officials from the Unite union have been locked in talks with the airline's chief executive, Willie Walsh, this week in a bid to find a breakthrough in a bitter row over cost-cutting.
A Downing Street spokesman said: "The Prime Minister believes that this strike is in no-one's interest and will cause unacceptable inconvenience to passengers. He urges the strike be called off immediately. He also urges BA's management and workforce to get together without delay to resolve what is a dispute about jobs and wages."
Unite's joint leader, Tony Woodley, said he was "extremely disappointed" that the efforts to head off a three-day strike from tomorrow had failed and accused BA of wanting a "war" with the union.
Mr Woodley emerged from five hours of talks with Mr Walsh at the TUC headquarters in London today to say that "hawks" on the BA board had won the day.
He said BA had tabled a worse offer than one withdrawn last week after the union announced this weekend's strike, and another four- day walkout from March 27.
"I am extremely disappointed for the travelling public and our members, but this union will now support our members, while remaining open for talks with the company.
"It is with great disappointment that I have to say the strike will go ahead. It is an absolute disgrace and an insult to our people that he (Mr Walsh) tabled a deal that reduced the amount of pay on offer.
"It is ridiculous to expect anyone to go to their membership with a worse offer."
Mr Walsh left the TUC a few minutes after Mr Woodley, describing the industrial action as "completely unjustified".
"It is deeply regrettable that a proposal I have tabled to Unite, which I believe is fair and sensible and addresses all the concerns of cabin crew, has not been accepted.
"The offer remains available, but it will be withdrawn once industrial action commences.
"Tens of thousands of BA people now stand ready to serve our customers. BA will be flying tomorrow and will continue to fly through these periods of industrial action.
"I remain available to talk, but our business must make changes. I am disappointed that the union have not been able to accept our sensible proposals."
Mr Walsh agreed that the new deal tabled in the current round of talks was not the same as the one withdrawn last week, arguing that BA had incurred "significant" extra expense because of the cost of its contingency plans and the number of passengers who have cancelled flights.
The financial value of the new offer was not as attractive as the previous one because BA had to recover the money it had lost.
Transport Secretary Lord Adonis said: "It is disappointing that the talks have broken down. This strike is in no-one's interests and will cause major inconvenience to passengers.
"Clearly, passengers travelling in the next few days will need to check with BA on the status of their flights. I continue to urge both sides to find a negotiated settlement."
Mr Walsh said he had given assurances to Unite about the airline's plans for pay and conditions of crew on new flights which he believed would have been accepted it it had been put to a ballot.
He confirmed that workers who joined the strike will lose their travel perks, which include flights at vastly reduced cost.
"That was an adult statement made to adult employees. We said we will not continue to provide perks to people who are prepared to inflict damage to our business."
Mr Walsh said BA would now put in place its "extensive" contingency plans, which include the use of 23 fully crewed planes leased from other companies.
"I am satisfied that our contingency plans are robust. We are very confident that we will continue to fly our customers in comfort."
Mr Walsh said it was "absolute nonsense" that he wanted to break the union, pointing out that he had been at the TUC for the past three days trying to agree a deal with Mr Woodley.
"We have spent 13 months in negotiations with the union. BA has been at the table, ready, willing and able to negotiate. If people want a scapegoat, they will have to look somewhere else."
BA said in a statement: "We are very disappointed that, despite lengthy negotiations, Unite has rejected the chance of a settlement and resolved that its strikes should go ahead.
"We are confident our cabin crew would accept our latest offer if Unite put it to them. In recent days, we have shown considerable flexibility in the interests of protecting customers from the effects of this completely unjustified industrial action.
"We have put forward proposals that would secure long-term pay protection for all existing crew, new opportunities for crew at Gatwick and modernisation of our industrial relations framework.
"Despite the recognition by the High Court that our changes to onboard crew numbers were valid and reasonable, we have also been prepared to make some modification to these changes to allow Unite to call off the strikes.
"It is a great pity that Unite continues to show such disregard for the interests of our customers and our business - and for public opinion at large.
"We will continue to strengthen our contingency plans to ensure that as many customers as possible can fly to their destinations during the strike period.
"We know that many cabin crew will work normally in the days ahead, and we look forward to their contribution - and that of tens of thousands of colleagues across the airline - as we keep our customers and our aircraft flying."
Mr Woodley accused BA of wanting to "go to war" with the union, adding: "The hawks have won the day. People who wanted to negotiate sensibly are being outmanoeuvred and outfought."
Picket lines will be mounted over the weekend at several entrances to Heathrow, the airport which will be hit hardest by the strike.
The union will hold a rally tomorrow at Bedfont Football Club in Bedfont, Middlesex, which will be attended by striking cabin crew.
A union spokesman said: "These Unite members understand the pressures the recession places on the company. But they believe BA's future and 40,000 jobs depend on it staying a premier airline.
"For over one year crew have tried to negotiate. They've even offered to save the service by making sacrifices - up to £62 million in savings - but BA under the management of Willie Walsh won't listen."
TUC general secretary Brendan Barber said: "I am of course very disappointed that, despite all the efforts of recent days, today's negotiations broke down without agreement. I had hoped that these talks with Tony Woodley and Willie Walsh would have reached a position that would have made it possible for the dispute to be resolved and the planned strikes called off.
"This dispute will, at some stage, have to be settled by negotiation and I will continue to explore with the parties any avenues to a settlement."
BA's new offer involved a four year pay deal, freezing wages in year one, giving 3% rises in years two and three and an increase in 2013/14 based on RPI inflation but capped at 4%, it was disclosed later.
BA also offered to reinstate 184 cabin crew on its Eurofleet and Worldwide services as well as guaranteeing that terms and conditions for current crew would be maintained.
A letter from Mr Walsh to Mr Woodley today, written before the talks broke down, said: "As you are aware, on a number of previous occasions we have agreed to work together to develop a different approach to industrial relations. Unfortunately local representatives have been unwilling to fully engage with us on this.
"It is clear that the company will only be able to afford this agreement if there is a stable industrial environment, without any further revenue loss or reputational change.
"We believe the best way of guaranteeing this is through fundamentally changing the industrial relations environment. This needs to begin with a radical, far-reaching review of our current ways of working."
Mr Walsh said he wanted to renegotiate the industrial relations framework by the middle of June, adding: "For the sake of our customers, our people and our business, it is time to move on and end this damaging dispute. You will see that the proposal is simple, clear and positive and as such I would like you to offer this to our people with your recommendation of acceptance.
"This is our best and final offer and will be withdrawn once industrial action commences. Following this our focus will then be on delivering for our customers during the strike."
Mr Walsh said in his letter to Mr Woodley that he wanted the union to agree not to take any strike action during the course of the proposed four-year agreement.
BA made record losses of £401 million in the 2008/9 financial year and a record loss of £292 million for the six months to the end of last September.
Shadow transport secretary Theresa Villiers said: "Labour's union paymasters at Unite are determined to inflict travel misery on thousands of families. It is disgraceful that they are going ahead with this unnecessary strike.
"Gordon Brown should do all he can to urge Unite, who are funding his general election campaign, to call off the strike. Or he should stop taking their money.
"Britain now faces Labour's spring of discontent with militant unions threatening to bring our railways to a standstill as well. Strike action could leave the country facing a serious transport meltdown."