Managers will attempt to deal with the post during the strike

The Royal Mail wants only essential items to be posted during the 24-hour walk-out over pay.

Members of the Communication Workers Union (CWU) are demanding a bigger rise in their London weighting allowance than that offered by management.

The Royal Mail is offering to increase the inner London allowance by �300 to �3,784 and the outer London allowance by �300 to �2,667.

But the union wants �4,000 a year for inner and outer London.

We have made a very fair offer and there is no more money to come - a strike will not generate more money, it will do exactly the opposite Royal Mail spokesman

CWU Deputy General Secretary David Ward said he expected "solid support" from the 25,000 London members of the union.

He said: "We want workers to earn a living wage in London without having to work all hours of the day or night."

Backlog of letters

Although the strike is only taking place in London, it could have a knock-on effect in other parts of the UK over the next few days.

About 82 million letters are posted each day nationally - 16 million of those are in London.

The strike will cost the Royal Mail up to �10m and it could take several days to clear the backlog of post.

The London Chamber of Commerce has said the strike will have a devastating impact on thousands of London-based firms, particularly small businesses.

A Royal Mail spokesman said: "We have made a very fair offer and there is no more money to come. A strike will not generate more money - it will do exactly the opposite."

A team of 4,000 managers will attempt to deal with the mail while the strike is taking place.