Dr Williams examined both of Mrs Clark's sons

Mrs Clark was convicted of murdering her sons Christopher and Harry in 1999.

She was cleared in 2003 after her appeal was told Harry had a bacterial infection which probably killed him.

But Dr Alan Williams, 58, who denies charges of serious professional misconduct, says he saw no signs of infection or inflammation.

That was my opinion and remains my opinion Dr Alan Williams

Mrs Clark had always denied smothering her first son, Christopher, when he was 11 weeks in December 1996 and shaking Harry to death in January 1998 when he was eight weeks old.

Dr Williams, a Home Office forensic pathologist from Plumley, near Knutsford, Cheshire, carried out post-mortems on both boys.

At first he said Christopher had died from a lung infection but changed his mind after Harry's death and claimed he was smothered.

The General Medical Coucil hearing heard that Dr Williams told Mrs Clark's 1999 murder trial that Harry appeared to have been shaken to death but he did not keep proper records of tests he carried out, throwing doubt on the quality of his work.

The 2003 appeal was told by prosecutors that Dr Williams was aware of microbiological tests which had shown that Harry had the bacteria staphylococcus aureus in his body, which was the most likely cause of death - but that he did not reveal this at her trial.

'Contamination'

At the GMC hearing, Dr Williams said he still agreed with what he had noted after carrying out the post-mortem on Harry in January, 1998 - that there was no evidence of acute infection or inflammation.

Asked by his counsel, James Turner QC, if that was his honest opinion, he said: "That was my opinion and remains my opinion."

Dr Williams, said factors including haemorrhages in the orbits of the eyes, swelling of the spinal cord and some bleeding gave him concern during his examination.

He insisted he was competent to work on eyes and the brain, and said it frequently happened that samples became contaminated with bacteria.

Earlier, the GMC hearing had heard allegations Dr Williams had been "slapdash" in his approach to the post-mortem.

Roger Henderson QC said: "It will be our evidence that the absence of a contemporaneous report of the ribs and the absence of any photographic record shows he had a slapdash approach.

"It may have been expected from a forensic pathologist that his findings might be the subject of an intense scrutiny and he would have to answer to his findings potentially in a coroner's court or a criminal court.

"As a matter of routine, Dr Williams should have been meticulous in his work."

Mr Henderson is representing former Tatton MP Martin Bell, who made an official complaint against Dr Williams. Mr Bell was Mrs Clark's MP at the time of her conviction.

The GMC had heard calls from James Turner, QC for Dr Williams, for the case to be thrown out or adjourned, due to a "scandalous delay" in bringing it.

The case continues.