A Midland MP campaigning for the release of "secret" hospital files on children who were the subject of controversial medical research is being threatened with legal action by a Staffordshire NHS trust.

John Hemming lodged an official complaint with the Speaker of the House of Commons after the University Hospital of North Staffordshire said it was prepared to sue him for thousands of pounds.

Mr Hemming (Lib Dem Birmingham Yardley) has been involved in a long-running dispute with the trust over the work of consultant paediatrician Professor David Southall, who in August 2004 was found guilty by the General Medical Council of serious professional misconduct and banned from engaging in any aspect of child protection work for three years.

Prof Southall - employed by the North Staffordshire trust and an expert on sudden infant death syndrome - carried out experiments in Stoke which examined the effect on babies of reducing the level of oxygen in the air they breathed.

Parents were told babies in the study, aged on average three months, faced "a small risk of sudden death" when given air with 15 per cent oxygen compared with 20 per cent in normal air. Despite protests over dangers, experiments on premature babies continued even though 28 of the babies involved in the project died.

Mr Hemming, who wants the North Staffordshire Hospital to hand over to parents the files on children who came into contact with Prof Southall, said: "The hospital have been keeping secret medical files called 'special case files' on some of their patients. It was recently agreed that these files would be merged with the normal medical records.

"I have been writing to the hospital asking them to tell patients when there is a secret medical file. The hospital's response has been to pass the issue to their lawyers.

"Their lawyers have now threatened to sue me for the cost of the legal advice. This is complete nonsense. The hospital should obey the law. If they don't know what the law is then they should not try to get me to pay the legal costs of them finding out."

In a House of Commons debate on December 19, Mr Hemming said the research conducted by Prof Southall over many years had been "just as damaging as that of Josef Mengele", the notorious Nazi doctor who conducted experiments on Jewish children.

Mr Hemming said parents of babies used in Prof Southall's study were given little choice in the matter.

"Notwithstanding many requests to his employer, the University Hospital of North Staffordshire, there has been no action to tell patients what has been happening.

"One of the most worrying aspects is that the records of babies who suffered sudden infant death give no indication of what was done to help them, such as giving additional oxygen to prevent the death. Parents were not asked for their consent to the experiments; they were merely told, in writing, that they would happen, without any details."

Mr Hemming added: "Dr Southall looked at the response of babies to asphyxiation, shortage of oxygen and the presence of carbon dioxide. The experiments were known as sleep studies, and started with about 7,000 babies born in the mid 1980s at Doncaster and Rotherham hospitals.

"Phases one and two of the experiments were quite reasonable. Phase three, however, involved choking babies for ten sessions of ten seconds, depriving them of oxygen by giving them only 15 per cent rather than the normal 21 per cent, and then giving them too much carbon dioxide.

"A large number of brain-damaged babies were born in Doncaster in the 1980s. However, the records showing which babies were in the experiments were not in the medical files, because Dr Southall kept secret files, known as 'special case files'."

A spokeswoman for North Staffordshire University Hospital NHS Trust said: "Our solicitors are dealing with this and it would be quite inappropriate to comment."