Two patients have died and three more are seriously ill after being mistakenly given the all-clear by two doctors drafted in from overseas to help cut NHS waiting lists.

An undisclosed number of colonoscopy procedures, an operation where a camera is inserted into the bowel to check for malignancies, have had to be reviewed after a specialist found cancer in an unidentified patient in January this year.

The total number who may be terminally ill is still unknown.

Steve Davies, 47, a father of three died in September last year after having previously been told he was healthy following a colonoscopy at Shepton Mallet treatment centre in Somerset, a private hospital which contracts with the local NHS to provide waiting list surgery and diagnostic procedures.

A second man died in January. Another man seen by the second doctor involved has come forward because of local publicity and discovered he has advanced cancer.Two more missed diagnosis have been identified by the review, carried out by a team of independent experts drafted in by the Department of Health.

The surgeon at the centre of the investigation is Ben Mak, a Dutchman who has spent much of his career operating on landmine and bullet-wound injuries for the Red Cross in Afghanistan, Sierra Leone and Angola.

As a result of concerns Mak was suspended and resigned in May. 1,828 colonoscopies performed by him between his arrival in Shepton in October 2005 and March 2008 have been reviewed by a team of independent experts drafted in by the Department of Health. 97 of them were considered sufficiently worrying to require patients to undergo immediate re-investigation for possible malignancy. Of the remainder, most have either been told to consult their GP as soon as possible, or to ensure they are rechecked within five years. Only 480 have been told there is nothing to worry about.

Colonoscopies carried out by another surgeon, have also been reviewed. Hospital authorities at Shepton Mallet insisted there was no evidence of misdiagnosis in this doctor’s work, but Stuart Bromley, an Exeter solicitor, says he has a client now gravely ill with cancer, who was told by the doctor in September last year there was no evidence of a tumour.

Colon cancer is one of the most common forms of the disease. It affects 23,000 people annually, of whom 16,000 die.

Experts say such tumours are normally slow-growing and can be detected on a colonoscopy up to four years before they become fatal.

Edwin Scarbrick, vice-president of the British Society of Gastroenterology, said NHS units and most private centres are now signed up to a national accreditation programme overseen by four of the medical Royal Colleges. This ensures colonoscopy diagnoses are regularly audited and reviewed.

It is not clear what audit system was used at Shepton Mallet, but the hospital’s annual report for the year to March 2008, reported no problems.

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