Waiting times are a key part of the performance ratings for hospitals

It comes after a backlog of patients waiting for treatment was discovered at the Royal National Orthopaedic Hospital in Stanmore, north west London.

The inquiry by the Strategic Health Authority (SHA) began after the hospital's performance rating dropped in the latest NHS league tables.

The SHA said they were working to ensure this did not happen again.

Targets to cut waiting lists and waiting times are a key part of the performance ratings for hospitals compiled by the Healthcare Commission.

Since these irregularities came to light the trust has been working to contact all affected patients Christine Outram, SHA chief executive

The hospital saw its performance rating drop from two to zero stars in the latest NHS league tables.

Last month it emerged that Stuart Coalwood, acting director of commissioning at the hospital, had been suspended pending the outcome of an investigation.

The hospital said it had identified about 300 patients who had been taken off the waiting list in the last year, mostly due to "valid reasons".

But the SHA said about 50 inpatients had been found to be waiting for treatment longer than the maximum period of nine months.

And about 450 outpatients were found to be waiting longer than the 17-week maximum waiting time.

Christine Outram, SHA chief executive, said: "Since these irregularities came to light the trust has been working to contact all affected patients and offer them an appointment before the end of July.

"It has been both our and the trust's absolute priority to make sure that all patients are seen as quickly as possible."

The inquiry panel was due to meet for the first time on Wednesday and is expected to report its findings in September.