HOPES of a breakthrough in the postal workers' dispute faded last night as union leaders and managers struggled to resolve a row which has crippled mail deliveries across the country.

Another day of talks failed to produce a solution to a conflict which has now spread across the UK.

A huge backlog of millions of items of mail continued to mount, forcing the Royal Mail to seal post-boxes in London.

More than 20,000 postmen and women remained on unofficial strike across the capital and in parts of Essex, the North-West, Hampshire, the Midlands and Home Counties.

Communication Workers Union leaders and Royal Mail managers met for almost 12 hours on Saturday and again for several hours yesterday, but optimism that a settlement could be reached was dashed.

The company's chief executive, Adam Crozier, unexpectedly joined the talks on Saturday night, dealing directly with the union's deputy general secretary, Dave Ward.

Both men said progress had been made and there were moves aimed at paving the way for a deal to be announced last night.

But in the event, there was little progress made and the two sides are due to continue negotiations today under the chairmanship of reconciliation service Acas.

Some union officials said media interviews given by Mr Crozier yesterday, in which he warned of possible legal action to try to end the wildcat strikes, had hit the chances of a deal.

Mr Crozier said the Royal Mail was facing increased competition and could not afford to put up with industrial action.

He also said that an increase to the London weighting allowance, which is at the heart of the row, could not be improved.

The conflict started two weeks ago when a number of drivers in Southall, west London, were suspended after returning to work from an official London weighting strike.

The union claimed the Royal Mail was trying to intimidate and bully workers into agreeing unacceptable working practices.

This was denied by the Royal Mail, which has said it was merely implementing a back-to-work agreement, which had been approved by the union.

Wildcat strikes have spread over the past two weeks, partly as a result of the Royal Mail trying to move bags of letters from strike-hit areas to other centres.