NHS managers are being warned not to exploit the dedication of nurses after it was revealed that three quarters of staff at Oxfordshire's largest hospitals worked extra hours.

In a Healthcare Commission survey carried out last year, 75 per cent of workers at Oxford's John Radcliffe and Churchill Hospitals and The Horton, in Banbury, said they spent time working beyond their contracted hours.

The findings follow the loss of 600 jobs at the Oxford Radcliffe Hospitals NHS Trust - which runs the three sites.

And the Royal College of Nursing is hoping managers are not taking advantage of the vocational disposition of its members to bridge holes in the workforce.

More than 500 staff took part in the survey, which showed that 80 per cent of nurses worked extra hours, compared with 60 per cent of administration staff.

It also revealed that 59 per cent of workers who do more than their contracted hours do not get paid - with some putting in an extra 16-20 hours a week free. The report said 83 per cent said they did it to provide the best possible care for their patients.

Dawn Chambers, the RCN's Oxfordshire officer, said: "It's not the sort of job where you down tools and walk out the door at 5pm. I would like to think no-one would take advantage of nurses' goodwill and dedication to their jobs. I'm not saying it doesn't happen, but I'd like to think it didn't."

An ORH spokesman said: "This is not new and, this year, fewer staff said they had worked longer than their contracted hours. As a trust, we have a responsibility to ensure staff aren't exploited and that they have a reasonable work-life balance."