Postal workers are preparing for a six-day rolling strike and have confirmed that a Christmas shutdown, the first in the Royal Mail’s history, could not be ruled out.

The Communication Workers Union leadership yesterday said it would be intensifying its action if a settlement with Royal Mail could not be reached.

Billy Hayes, the general secretary, said they would be “upping the dispute...not scaling it down.”

His deputy Dave Ward said that a Christmas strike would be “very difficult call” for the union to make, adding: “I’d rather sort this out now than have people think we’re holding them to ransom.”

After the Royal Mail fiercely blamed the union for the breakdown of this week’s talks, yesterday the union came out fighting.

Mr Ward said the modernisation changes being planned by Royal Mail could lead to 60,000 jobs being lost and the remaining workforce moved from full-time to part-time As up to 47,000 of its members took strike action yesterday — with another 400 today and up to 77,000 on Saturday — the leadership did hold out an olive branch yesterday and held off naming new strike dates. It has to give the company seven days' notice.

Options under consideration include a complete 48-hour stoppage involving all its members or a rolling six-day action that would mean each member striking for two days.

Efforts were under way to get both sides back to the TUC for further discussions.

A backlog of 30 million letters caused by two strikes last week had been reduced to less than two million, according to the company.

Mr Higson said he was confident delayed mail caused by the new walkouts would be cleared by early next week.

David Frost, director general of the British Chambers of Commerce, said: “No one is benefiting from ongoing industrial action and hard-pressed businesses are the innocent victims.

“With the country still in recession, this really is a poorly timed strike. Companies simply cannot rely on the postal service, and Royal Mail is paying for it in lost contracts and revenue.”

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