Lord Mandelson has lambasted the postal workers’ union ahead of a three-day strike in London starting on Wednesday, accusing it of blocking change at Royal Mail.

The business secretary’s frustration over his stalled plans to part-privatise the postal operator became evident as he accused the Communication Workers’ Union of “boycotting” a 2007 agreement between the union and the company to modernise the company. “I realise that’s a very serious charge to make but any other conclusion is impossible to reach,” he asserted.