The strike, which will affect deliveries, collections and mail processing throughout the capital, is to be held by members of the Communication Workers Union (CWU), which represents most of Royal Mail's 150,000-strong workforce. It claims Royal Mail is making "arbitrary cuts" without its consent.

Speaking about the proposed strike action, Dave Ward, CWU deputy general secretary, said: "Royal Mail is blocking modernisation by refusing to negotiate change with the CWU.

He added: "We have offered a moratorium on all strike action if Royal Mail will suspend executive action and enter into meaningful negotiations.

"There is growing unrest across the country as Royal Mail tries to impose damaging cuts and changes without the input of union reps. The future of the business must be safeguarded through careful planning, not shooting from the hip."

Royal Mail said in a statement that the strike "is completely at odds with its repeated claim to support modernisation and to introduce new ways of working throughout the business".

Business secretary Lord Mandelson has previously said the proposed part-privatisation of the operator was "vital to sustaining the universal service".