Some of the most skilful surgeons in the health service, who also have the longest waiting lists, are spending only seven hours a week operating.

Orthopaedic surgeons, who operate on backs, bones and joints, are conducting an average of just over six operations during a working week of 50 to 60 hours, according to a study. There are almost 250,000 patients waiting for orthopaedic surgery, one-quarter of the total NHS waiting list.

The finding raises urgent questions about the best way of spending the extra £19bn pledged for the NHS over the next four years in last month's budget. Medical organisations have demanded extra surgeons be appointed to cope with growing workloads but the study, done by Professor John Yates of Birmingham University, suggests big gains could be made by reorganising their work.

One proposal is to open operating theatres from 7am to 6pm instead of the usual 9am to 5pm. Surgeons are often prevented from operating by shortage of theatre time and staff and by the growing burden of administrative work. They also have to take out-patient clinics and train junior staff.

Professor Yates, director of Inter-Authority Comparisons and Consultancy, said: "We have to ask what the NHS is doing when it has got key people with world-class skills and it is only getting seven hours a week of those skills. We wouldn't do that with a bus driver."

His study of 182 surgeons in two NHS regions, published in the Health Service Journal, found one-fifth were working below the minimum of three half-day operating sessions a week recommended by the British Orthopaedic Association. Although 37 per cent operated for eight hours or more a week, 11 per cent operated for four hours or less.

"The Government is talking of investing huge extra sums in the NHS. One way would be to employ 250 extra surgeons. But if each of the existing surgeons did one extra operating list [half-day] a week, that would be equivalent to 250 extra surgeons. This is not my idea - some surgeons out there [are] now doing eight, nine, 10 and 11 hours' operating a week."

Orthopaedic surgeons can double or treble their NHS salaries with private work in the evenings or at weekends and NHS managers complain it is difficult to negotiate with them when they are earning sixfigure sums in their spare time and only £60,000 to 70,000 for a 50-hour week in the NHS.

Professor Yates said: "I tried to arrange an appointment with one surgeon and was told he did not work for the trust on Thursdays or Fridays. He was maximum part-time, meaning he is supposed to devote substantially the whole of his time to the NHS. He probably worked very hard to get his NHS contract fulfilled from Monday to Wednesday. He told me he could earn £1,500 for a half-day operating in the private sector. If he did four sessions a week, 40 weeks a year, that would be £250,000."

The number of orthopaedic surgeons working in England has risen by more than 50 per cent in the past decade, from 678 to 1,023, but their productivity has declined. Each surgical team is now seeing fewer out-patients and in-patients than 10 years ago.