Gordon Brown and Lord Mandelson will plead with British Airways (BAIRY) and the Unite union over the next 24 hours to return to the negotiating table so the cabin crew strike due to start on Saturday can be called off.
In a two-pronged approach, the Prime Minister will hold private talks with the union's leadership, while Lord Mandelson, the Business Secretary, will speak to BA management. Two "go-betweens" will press both sides to make a last-minute effort to avert the industrial action: Brendan Barber, the TUC general secretary, and the conciliation service Acas.
"We have 24 hours to avert the strike, and that is what we will try to do," one government source said last night. "We can't negotiate but we can urge both parties to do so. It's not enough to patch over it so we postpone this action. The two sides need to reach a permanent settlement once and for all. Every time the union threatens action, BA loses customers. It is ruinous for BA. The union has it over a barrel."
However, hopes of last-minute talks receded when BA raised the stakes by refusing to guarantee it would not sack union officials at the heart of the dispute. That heightened union fears of a clear-out of shop stewards at Bassa, Unite's cabin crew branch. Seven members of its committee face disciplinary proceedings launched last year.
Unite has attempted to elicit support for industrial action from around the world, and has held talks with bosses from the Teamsters union, which boasts 1.4 million members, in Washington DC, after which Teamsters bosses said they would not rule anything "in or out" when it came to supporting the British strike. Union bosses in Australia and at the German organisation ver.di have vowed to support any industrial action by making it hard for strike-breaking volunteer staff to work in airports.
Ver.di's members say they would refuse to cooperate with strike-breaking staff on flights during the walkout from March 27.
A BA spokesman said it was sad to see the union attempt to get overseas backing for "unjustified strikes against an iconic British brand."
A Teamsters spokesman said: "The Teamsters are an active member of the International Transport Workers Federation. ITF affiliates around the world are mobilising to support British Airways workers in their fight for passenger safety and worker respect."
A small number of cabin crew members used a secure online forum yesterday to question whether the strike should go ahead. "Unless we get concrete proof that we will not be sacked, we should call off the strike on Friday," said one. Another urged colleagues to accept the deal offered by BA. "It is not far from [our demands] except for the losing of the crew member and we don't have to take the pay cut."
Although the Tories believe the BA dispute will damage Labour's prospects at the general election because of the party's links with Unite, Labour sources claim the issue is not "playing hard on the doorsteps" because ministers have criticised the strike.
In an attempt to embarrass Mr Brown, the Tories and Liberal Democrats are targeting Charlie Whelan, Unite's political director and a close ally of Mr Brown as his press secretary when he was Chancellor. Last night Mr Whelan insisted he was playing no part in the dispute. "I'm not going to hide away or skulk because the Tories want to turn me into some kind of bogey figure," he told the website leftfootforward.org. "I'm working legitimately in a trade union, trying to help the Labour Party win a general election."
The Tories are drawing up plans to target Labour's links with Unite, and other major union backers, throughout the election campaign. They will portray the unions as the real power-brokers within the Labour Party, citing the number of MPs they sponsor and their alleged influence over policy.
Conservative sources said Labour was "massively vulnerable" on the issue and are keen to evoke memories of the party's troubled relations with the unions in the 1970s.
The Conservatives also hope their planned "relentless focus" on the union will neutralise the continuing Labour onslaught on the Tories' reliance on money from their deputy chairman Lord Ashcroft.
Michael Gove, the shadow Education Secretary, said: "We will continue to stress we are the party of reform, while Labour is in thrall to big unions that will take us back decades. It will be a consistent theme."
He added: "It goes beyond Labour's links with big unions; it goes to concerns that Labour has returned under pressure to its ideological comfort zone. It undeniably is the case that Labour's political agenda is more and more being dictated by the unions."
David Cameron fired the opening shots of the attack in acrimonious exchanges yesterday with Mr Brown at Prime Minister's Questions.
The Tory leader accused Mr Brown of acting in the "union interest" rather than the national interest over the BA strike and challenged him to call for cabin staff to cross picket lines this weekend. He described Labour as a "wholly owned subsidiary of the Unite union" and denounced Mr Brown's "hand wringing" as proof of weakness.
The Prime Minister retorted that Mr Cameron's comments were "calculated to provoke" the dispute, not settle it. He said: "It is complete opportunism. They should be trying to find a resolution to this dispute. They should be calling on us to work with the unions and the management. Anything else is likely to inflame the situation."
The Tories pounced on the disclosure yesterday that a senior Downing Street official's salary is paid by Unite. Clare Moody, a national officer with the union, works in No 10's political office.
Nick Clegg, the Liberal Democrat leader, accused Mr Whelan of being like Lord Ashcroft in trying to "buy seats."
BA yesterday announced it would increase the number of flights during the first strike period because of growing numbers of cabin crew volunteering to work. Originally it said 60 per cent of passengers would be flown to their destinations during the three days of industrial action. It revised the forecast to 65 per cent and said more than 60 other airlines were offering to carry BA passengers whose flights were grounded.