Hopes of an eleventh-hour deal to avert the BA strike were receding last night despite Gordon Brown urging the Unite union to call off its action.

The Prime Minister put himself on collision course with Labour’s biggest financial backer when he said that Unite’s proposed walkout was “unjustified and deplorable”.

However, despite hopes in Downing Street that both sides would return to the table, neither was prepared to budge.

Unite said last night that it might be prepared to suspend seven days of planned unrest if BA put a last-minute offer that it withdrew last week back on the table. However, the company told the union that it had no intention of doing so.

The stand-off left Mr Brown looking to distance himself from the strike, which threatens to disrupt the travel plans of hundres of thousands of passengers in the run up to Easter, shortly before he calls the election. “It’s not in the company’s interest, it’s not in the workers’ interest and it’s certainly not in the national interest,” Mr Brown told Woman’s Hour on Radio 4. It was, he said, “the wrong time” — a reference that could have been as much about the expected May 6 election day as the Easter holiday.

Labour finds itself increasingly entangled in an industrial dispute on the opposite side from the union that is funding much of its campaigning in marginal seats.

Unite, the country’s largest union, has given Labour £11 million over the past four years and helped it to stave off bankruptcy by underwriting its debts.

Charlie Whelan, Unite’s political director, is Mr Brown’s former spin-doctor and is being lined up for a role in the Labour election campaign.

The union and Downing Street played down suggestions that the clash would hamper Labour’s campaigning on the ground, where Unite members are leading the telephone polling of swing voters in Tory target seats. But the Tories seized on Mr Brown’s unease and called on Labour to sever its financial links with Unite.

George Osborne, the Shadow Chancellor, said: “Gordon Brown cannot have it both ways. He cannot condemn the strike while at the same time taking money from the strikers’ union. In the end, it’s a question of leadership for Gordon Brown.”

Mr Brown’s spokesman insisted that although the Prime Minister had changed his rhetoric, he had always believed a strike would be wrong.

Lord Adonis, the Transport Secretary, said that attempts to politicise the dispute would make it harder to resolve. “This is an industrial dispute, not a political dispute,” he said.

It is understood that Mr Brown has spoken to Willie Walsh, the BA chief executive, in recent days. He has also spoken to Tony Woodley, the joint general secretary of Unite.

A Unite source said Mr Brown’s intervention yesterday was a sign that Downing Street realised the strike was going to go ahead.

“I think Mr Brown has given up the ghost of trying to find a negotiated settlement and he is now engaged in political positioning,” the source told The Times. “There is nothing that is going to change the position. If the Prime Minister has a cunning, Baldrick-type scheme, then let’s have it. Getting a deal back on the table is an absolute prerequisite of moving forward. At the moment there is nothing.”

In a copy of the BA proposal, leaked by the union, the airline offered to replace one in ten of the cabin crew who left in November as part of a £62 million cost-cutting drive, and promised a two-year pay rise. Some overseas allowances would be cut and the airline demanded the right to separate negotiations with new recruits.

Unite sources accused Mr Walsh of being determined to break the hold that the union has at the company, where 97 per cent of cabin crew are members. Many BA cabin crew members feel that Mr Walsh is no longer interested in finding a negotiated settlement as the airline suffers its second-consecutive year of multimillion-pound losses.

Mr Walsh has already warned that he will be forced to implement deeper cuts from the cabin crew budget if the strike goes ahead.

Mr Woodley said: “The mood music here doesn’t allow me to feel that we have got a company that wants a settlement. This company doesn’t want to accept an offer, I feel. It wants a war. It wants to take on our members. I hope I’m wrong, but I don’t think I’m wrong.”

A BA spokesman said that there was no immediate prospect of renewed talks, despite the Prime Minister’s remarks. “We welcome his comments, but there has been no further movement so far,” the spokesman said.