British Prime Minister Gordon Brown waded into the acrimonious dispute between British Airways PLC and its cabin crew on Monday, calling a planned strike by workers “deplorable” and urging union leaders to cancel the walkout.

Speaking on Radio 4′s Woman’s Hour, Gordon Brown said the walk-outs should be called off. The strongly-worded stance puts him on a collision course with members of Unite, the country’s largest union – and one of Labour’s biggest donors.

The union has given £11million to the party over the last four years and boasts 160 members within Parliament.

Also, its political director is Mr Brown’s close ally and former spin doctor Charlie Whelan.

Until today, the Prime Minister faced walking a tightrope between avoiding upsetting his union paymasters and intervening in a damaging pre-election BA strike.

The intervention by Mr Brown follows the forthright comments made by Transport Secretary Lord Adonis yesterday.