British Airways has announced emergency plans to keep 60 per cent of its customers flying during a planned cabin crew strike this weekend - either on its planes or other airlines - as the dispute threatened to hit Labour's general election campaign.

With little sign of a breakthrough in the dispute between BA and Unite, the British Prime Minister was dragged into a bitter political row over the party's links with the unions.

Following accusations that the Government had minced its words for fear of antagonising Unite, Gordon Brown finally condemned the threatened strike as "unjustified and deplorable".

The union has announced seven days of action by cabin crew over pay and staffing levels - on March 20, 21 and 22 and from March 27 to 30.

BA has drafted in more than 1000 temporary cabin crew. It aims to fly 45,000 passengers each day during the first three days of industrial action. Thousands more would be offered seats on alternative flights.

Ministers are aware that a round of strikes orchestrated by Labour's biggest paymaster on the eve of the general election campaign would hand a propaganda gift to the Conservatives. Unite has donated £11 million ($23.5 million) to Labour since 2006.

Toughening his language, Brown said:

"It is the wrong time, it is unjustified, it is deplorable. We shouldn't have a strike. It is not in the company's interest, it is not in the workers' interest and it is certainly not in the national interest. I hope this strike will be called off."

Tony Woodley, the joint general secretary of Unite, said: "It is rather unfortunate that politicians of all parties always want to kick the unions and kick the employees when, in actual fact, it's my members who've been kicked here."

Brown's comments also provoked a backlash from Labour MPs. Jim Sheridan urged his leader to "take a step back and have a measured approach to this".

Baroness Hanham, the shadow transport secretary, said Labour should stop taking money from Unite. She said that Charlie Whelan, Unite's political director, was close to Brown and "up to his elbows in Labour's general election campaign".

The Transport Secretary, Lord Adonis, claimed such comments made it harder to hammer out a solution.

"This is an industrial dispute. It is not a political dispute. I deeply regret the attempt by the Conservative Party to politicise the dispute, which will make it so much more difficult for it to be solved in the way we all wish it to be."

BA said that during the first three-day strike by Unite, it will operate all long-haul flights and more than half of short-haul flights to and from Gatwick.

At Heathrow, the airline will operate 60 per cent of its long-haul flights. BA will not publish its schedule for the second tranche of strikes, March 27-30, until managers can assess how the initial plans worked.

Notable omissions from the emergency schedules are Singapore and Tokyo, although BA's alliance partners, JAL and Qantas, are expected to pick up many of those passengers.

Short-haul travellers from Heathrow are the most heavily affected. Even with aircraft chartered in from the low-cost carriers Jet2 and Transavia of Holland, BA can guarantee only 30 per cent of its schedule.