Managers said the mistake has been rectified

But Mr Charles said executives ill-treated patients and the CHC in the way they made the announcement.

"This has been distressing for patients. Somebody looks methodically for these errors, who has considerable skill and electronic aids, to make sure this doesn't happen.

"These patients are recovering from cancer treatment - not being open will mean that mental health problems could be added on top of their physical problems.

"It's unacceptable, the patient watchdog has a statutory right to be informed about the delivery of patient care.

"A lot of people would say this was a cover up.

"It's a schoolboy mentality, you've done something naughty so lets try and hide it away before somebody finds out."

The trust admitted that some women given treatment between April 1999 and July 2001 had since died but said the numbers where no higher than expected.

Explanation demanded

But a hospital spokesman admitted there was a "slightly greater risk" that the cancer could return for the women given the wrong dose.

Executives emphasised that not all women treated during the period were given the under dose.

Letters were sent out on Monday to patients offering them advice sessions.

The hospital has also said it was not in a position to tell the CHC anything until patients has first been informed.

A committee meeting of the CHC on Tuesday recommended writing to Mr Milburn in protest at the lack of communication.

At further meeting on 23 Janurary, the CHC may decide to make the complaint.

Computer flaw

After a meeting with medics and managers from the trust on Tuesday, Mr Charles said the treatment failure was caused by human error.

Medics had problems with the computer software which calculated the radiotherapy dose.

But he added that statistics shown to him by the trust delegation indicated there was almost no increased risk of the breast cancer returning.

"I was greatly reassured, the risk of the cancer returning is so small it's unlikely that anybody has been affected at all," he said.

He added that 72 of the 132 patients had contacted the trust or NHS Direct since letters were sent to them and all were satisfied with the contents.