Postal workers leaders will announce dates today for national strikes in a bitter row over jobs, pay and conditions after hopes of a last-ditch deal faded.

The Communication Workers Union had launched an 11th hour bid to avert nationwide walkouts, giving a deadline of today for a breakthrough in the long running dispute.

The union will have to give seven days notice of a strike, so the earliest stoppage will be October 22.

More than 60 Labour MPs yesterday publicly backed the union's offer, while one attacked Business Secretary Lord Mandelson and Postal Affairs minister Lord Young over their opposition to the CWU.

At Prime Minister's question time, Labour's Dave Anderson (Blaydon) asked Prime Minister Gordon Brown: "Do you agree with me that the best way to resolve the Royal Mail dispute will be to get the parties around the negotiating table?

"If you do, then will you tell Lords Young and Mandelson to start to concentrate on that and stop attacking the CWU?"

The Prime Minister said the Royal Mail could lose major contracts if the "unnecessary" walk-out was not prevented.

"We want to see a settlement of this dispute. But we want to say that this dispute is not in the interests of anybody.

"If Royal Mail start to lose major contracts, like those of some of the major firms in this country, it will be difficult for them to regain these contracts over a short period of time.

"I know that Government ministers are working actively to make sure that the parties, the management and the workforce are negotiating.

"I hope that they will do so and I hope that this unnecessary strike can be prevented."

A Royal Mail spokesman said: "The CWU's so-called peace offer is a list of threats and demands against Royal Mail, including a demand for more money and an absolute veto over any future change and modernisation, which no company would give.

"We challenge them now to offer genuine peace by honouring the promise they made for a no strike moratorium in return for a period of no change as they are very well aware that we said two weeks ago that we would make no further changes until the New Year."

Billy Hayes, CWU general secretary, said: "Our offer included a three-year proposal to secure stability for the Royal Mail.

"Royal Mail was too quick to reject our offer and this questions the company's intentions to resolve the dispute. The company needs to engage with these issues to reach a resolution."