Mandelson, who has been pushing for the proposed restructure, has said the bill was being "jostled" for space within current government legislation.

Although the business secretary wants the bill to go through before the summer, he told the BBC that it is now likely to be "later" than that.

Another factor for the delay is the state of the economy, according to Mandelson. Speaking to the Financial Times, he said: "I have to concede that the original linking of the legislative passage and the bidding process for the strategic partner has been decoupled."

The delay is the latest stumbling block for the part privatisation following opposition from Labour backbenchers and possible bidders, Deutsche Post and TNT, curtailing their interest in the mail operator.