Dave Ward, deputy general secretary of the Communication Workers Union attacked Mr Crozier, and Royal Mail chairman Allan Leighton for "managing decline" in the face of competition.

Mr Ward told his union's annual conference in Liverpool that the leadership of the Royal Mail, and the management's business plan were both in "crisis."

He went on: "One week the company is in crisis, then they announce there has been a fundamental turnaround, then they are in crisis again."

Mr Ward attacked the £3 million salary paid to Mr Crozier as "obscene", adding: "It is unacceptable and he has to go. The business needs a new vision to succeed.

"Royal Mail is doing the Oliver Twist thing by asking the Government for more money to pay for pensions and to transform the business.

"They want between £8 billion and £9 billion from the Government, which they know will not be given, so they will come out and say the only solution is privatisation.

"They are managing decline, and their business plan will not succeed, but we have these people on the run and I am convinced that if we carry on being united we will get rid of them and come up with solutions to secure our members' future."

The threat of industrial action over pensions is expected to increase when delegates discuss holding a ballot over the "unacceptable imposition" of pension reforms.