More than a third of first class post arrived late in an Oxford Mail investigation into Royal Mail’s service.

Tests by the paper showed just 65 per cent of first class letters achieved the company’s next day delivery standard – compared to its target of 93 per cent.

It is a worse result than last year’s test by the Oxford Mail, when 80 per cent of psot arrived on time.

Last night customers said they were disappointed but not surprised at the results. And they fear the service will deteriorate when the city’s mail will be sorted in Swindon.

But Royal Mail dismissed the survey as unscientific and said its own tests showed 92 per cent of first class mail arrived on time.

The Oxford Mail arranged for 55 letters to be sent to its Osney Mead offices from around the city, county and the rest of the UK on Thursday, March 12, and Friday, March 13.

Thirty-six letters arrived the next day, 11 arrived within two days, and the final eight were received three days after they were first posted.

Only 62 per cent of post sent from within Oxfordshire arrived on time.

Post from outside the county proved slightly more reliable with a next-day delivery rate of 68 per cent.

Robert Pineiro, marketing manager at Critchleys accountants in Paradise Square, Oxford, said: “We’ve had wet and damaged post which we told Royal Mail about last year and we’ve heard nothing back since.

“We’ve also had incorrect delivery of mail, which again they said they were looking into and again we’ve heard nothing back.

“We often get late post which put us at risk of fines from HM Revenue and Customs.”

A Royal Mail spokesman said: “It is difficult to rely on such a small sample, which is why Royal Mail spends more than £5m a year and sends more than 100,000 test letters a month to provide a statistically representative picture of our performance.

“Our quality of service results are independently researched on Royal Mail’s behalf, and the validity and accuracy of the quality of service data are accepted by Postcomm, the independent regulator for postal services in the UK.”

Diana Gough, 66, from Mill Street, Eynsham, whose late husband Desmond worked for the Royal Mail for 42 years, said she was unsurprised by the Oxford Mail’s findings.

She said: “You never know when the post is going to come. Some days it’s 9am, sometimes it’s 12pm.”

In June, Oxford’s sorting office in Garsington Road, Cowley, will close and transfer to Swindon.

Royal Mail claimed the move will improve services in Oxford.

Mrs Gough said: “The move to Swindon will make things so much worse.

“You only have to look at the traffic some mornings to know that.”

City councillor Patrick Murray has been contacted by Royal Mail customers in Barton Road Flats, Headington, who have complained about the service.

He said: “Some people have been left waiting for weeks for letters, and I know one resident has never got some of the packages he ordered off the Internet.”

Royal Mail has talks with Oxford City Council about changing an automatic time lock on the doors of the flats.

Nigel Woods, from Consumer Focus, which replaced Royal Mail pressure group Postwatch in October, encouraged customers to claim compensation and added: “Delayed mail is annoying, and in some cases can cause distress.”

“Compensation payments and poor complaint figures generally will be an additional incentive for Royal Mail to minimise delayed mail and improve their standards.”