Postal workers return to their jobs tomorrow determined to keep fighting after another day of strike action.

Delivery offices across the county were closed today as hundreds of staff backed an official national one-day stoppage.

And next week, delivery offices are set to be closed for 24 hours from 7pm on Friday, while staff at the main Oxford mail centre sorting office at Cowley will come out on Thursday night, according to the Oxford branch of the Communication Workers Union.

CWU representative Bob Cullen said: "We are deliberately choosing different days of the week because it is more disruptive."

Mr Cullen added that just six agency staff were being used to help clear backlogs of mail, in contrast to reports of larger numbers being used in other sorting offices around the country which has provoked further wildcat action.

At the centre of the national industrial action is a dispute over a pay increase and fears regarding privatisation.

Royal Mail managers say they need to modernise in order to survive, but staff say proposals will lead to increasing automation and ultimately 40,000 job losses.

Staff were on the picket line at the delivery office in Becket Street, Oxford, and at the delivery office in Sandy Lane West.

Roger Collins, a spokesman for the Communication Workers' Union at the Becket Street office, said 110 workers were on strike.

He added: "At present, there is no negotiation with management - they say they will meet us only to explain their position."

Meanwhile, the Royal Mail is disputing claims that millions of letters are being left unsorted, causing delays approaching two weeks.

Spokesman Sue Dakin said: "We are not disputing the fact there are delays, but in terms of moving mail, the numbers of unsorted items are in the hundreds of thousands rather than millions."