National strikes by postal workers will go ahead tomorrow and Friday after hopes of reaching a last-minute deal collapsed.
Up to 120,000 members of the Communication Workers Union (CWU) will stage two 24-hour walk-outs, crippling mail deliveries across the country.
The union warned of further strikes in the coming weeks and launched an extraordinary attack on Business Secretary Lord Mandelson, saying he was working "hand in hand with the Royal Mail" to "undermine the dispute".
General secretary Billy Hayes accused him of being the "minister without responsibility".
Dave Ward, the union's deputy general secretary, said the Royal Mail had no intention of resolving the dispute and seemed intent on "sidelining" the concerns of postal workers.
Mr Ward, who led the union's negotiators during marathon peace talks, said he believed progress had been made and that a deal could have been agreed which would have averted the strikes.
But he said a letter sent today to the union by Royal Mail managing director Mark Higson had "wiped out" progress which had been made during the talks and scuppered the chances of a deal.
Mr Ward said the letter from Mr Higson "completely contradicted" some of the issues that had been agreed during the talks and it appeared that he had a "veto" over the talks.
Mr Ward went on to claim that every time progress had been made during the negotiations "external forces" had deliberately attempted to undermine the chances of a deal.
He singled out three men - Mr Higson, Royal Mail chief executive Adam Crozier and Lord Mandelson.
"What we have seen in the last few days is a deliberate choreograph that tells us that the Government and the Royal Mail are working hand in hand to avert any chances of reaching a solution."
Mr Ward said he had met Lord Mandelson nine months ago when the Government was attempting to part-privatise the Royal Mail and was told that the minister had no confidence in the company's board and management, saying they did not have the skills to transform the company.
Lord Mandelson said the only way industrial relations would improve was if Dutch company TNT was brought in to help run the business, Mr Ward claimed.
He went on: "We are absolutely clear that the real truth behind this dispute is that Lord Mandelson clearly feels it is pay-back time because we defeated him on privatisation.
"Lord Mandelson is backing the same people he said did not have the expertise to deal with the transformation of the business."