A backlog of almost 50 million letters was awaiting clearance last night after agreement was reached to end a wave of wildcat strikes by postal workers.

Post boxes remained sealed in some parts of the country amid estimates that it could take up to two weeks to deliver all the mail held up by the industrial action.

About 15,000 workers joined the unofficial walkouts in several regions, including London, the North-East, the North-West, and Kent, paralysing 19 mail centres and 72 delivery offices.

In the North-East, about 250 workers took part in an unofficial strike yesterday.

Staff at Tyneside Mail Centre at Team Valley in Gateshead walked out in the early hours of the morning as a direct response to walk-out in Stockton and Middlesbrough on Monday.

This arose after workers were sent home for refusing to deliver General Election campaign material.

Managers stepped in to operate sorting machines and deliveries were still made although there were some delays.

The North-East action coincided with the wave of unofficial strikes at mail centres and delivery offices across the country, sparked by a dispute at Watford.

Members of the Communication Workers' Union at Watford voted to end their action yesterday afternoon after talks with Royal Mail officials.

An agreement was reached on Tyneside a few hours later and staff returned to work at around 4pm.

Workers at Stockton and Middlesbrough also returned to work yesterday.

Bob McGuire, CWU North-East representative, said: "We are pleased that we got a successful resolution to the problem."

A spokesman for the Royal Mail said: "Disruption to services has been kept to a minimum with deliveries being made across Northumberland, Tyneside and Wearside and collections have also been made."

He expected most deliveries to be made as usual today and that services would be fully restored by tomorrow.