In its latest report, published today, the commission says more than a third of patients - 36 per cent - criticised the time they had to wait for appointments, and then for results, as well as poor waiting room facilities.
But the number of unnecessary X-rays are both potentially dangerous to patients and use up money that could be better spent on other services, the report, Improving your image, says.
"Ionising radiation is dangerous and must be controlled. Twenty per cent of X-rays were clinically unhelpful. GPs may feel a basic X-ray is worthwhile simply to reassure a worried patient that `something is being done' - in effect offering a technical placebo. In the hospitals, junior doctors may understandably request examination in the absence of a consultant `to be on the safe side'."
Every year, £600m is spent on radiology services, which now include not only conventional X-rays, but also ultrasound, computer tomography, and magnetic resonance imaging scanning.
Andrew Foster, controller of the commission, said: "It costs between £15 to £25 for each X-ray including staff and overhead costs. But we found that in 20 per cent of cases it was questionable whether the X-ray was really needed. Often the X-rays were not even looked at by the consultants.
"Sometimes an X-ray is taken when one was carried out on the same patient only the day before.
"X-rays are an essential part of patient care. Most departments provide a highly professional service but many will need better management if they are to cope with growing demand. And trusts will need to manage capital better if patients are to benefit fully from future technology," he said.
Most hospital X-ray departments represent assets worth about £2m. The workload in NHS X-ray departments has gone up by 300 per cent since 1970, putting pressure on staff, but the commission found considerable variation in the number of hi-tech scanners available round Britain. Some health regions, including north London, have four times the number of MRI scanners per million population as others.
Ross Tristem, director of the NHS Trust Federation, said: "We welcome this report as a great opportunity to improve the quality and efficiency of radiology services.
"Subsequent local audits should enable trusts to examine the operation of their own services and agree action to secure more efficient and effective services for the future. We are certain that savings can be made, but it is doubtful that they could be as large as those envisaged by the commission.
"The federation has for a long time been urging a proper debate on the planning of capital requirements and the management of assets in hospitals and in the NHS as a whole. This is particularly true for capital intensive services like radiology, and we are glad that the commission raises these important questions."
Improving your image: How to Manage Radiology Services More Effectively, Audit Commission,HMSO; £11.Reuse content