NHS managers are monitoring flexi-time packages for nurses at Oxfordshire's major hospitals, to make sure the scheme does not jeopardise patient care.

More than a third of nursing staff at Oxford's John Radcliffe, Churchill and Radcliffe Infirmary, and The Horton, Banbury, work part-time, allowing them to take breaks during school holidays.

The scheme has already been blamed for causing the county's highest postponed operation figures for two years, during February's half-term break.

And managers are now trying to strike a balance between convenient nursing hours for staff and the best possible patient care.

There are 2,210 nurses employed at the four hospitals, overseen by the Oxford Radcliffe Hospitals Trust, and 840 have been tempted to stay within the NHS with flexi-time contracts.

But the scheme leaves wards under-staffed during holidays, forcing managers to close beds and subsequently cancel scheduled operations.

In February, 274 patients were told their operations would have to be postponed. In the same month, during the half-term week of February 19 to 25, there was an increase in empty beds.

Although weekly bed closures usually total between 60 and 100, in half-term week there were more than 130.

Tricia Hart, chief nurse for the Oxford Radcliffe Hospitals Trust, said: "All holidays suffer from the same issues. Thirty-eight per cent of our nurses are on part-time contracts and so a lot of people do then take their leave at the same time."

Despite the problems, the trust said it was important that nurses were given shifts which suited them if they were to be enticed back to Oxford's hospitals.

Spokesman Helen Peggs said: "If they weren't on term-time contracts in the NHS, they would be working for an agency at times when they wanted to anyway.

"We need to ensure that patient care is at optimum level at all times and that we have sufficient nursing cover, but we also need to strike a balance between this and allowing nurses to work when they want to. Clearly this is something we need to keep an eye on.

"We mustn't reach a point where patient services are put in jeopardy. We would continue to argue that, yes, the half-term break was a contributing factor to the problems in February, but there were other things to consider as well, such as illness."