BBC Midlands Correspondent Daniel Boetcher: "The government has ordered an urgent inquiry"

The treatment was applied to 122 premature babies between 1989 and 1993 at the North Staffordshire Hospital - 28 died and 15 suffered brain damage.

The investigation, ordered by Health Minister Baroness Hayman, will focus on the way the clinical trials were set up.

The study carried out at the Stoke hospital involved a new type of ventilator, which is now no longer used for premature babies, but is still used for older infants.

Mother Debbie Henshall says one of her children died and a second was left a quadriplegic.

Debbie Henshall: "They certainly didn't get consent from me"

She said: "I didn't find out until my second daughter, who had received the treatment, was four years old that the treatment was part of a trial and the equipment was experimental.

"I find that incredible. I just can't believe they can do that. I know my way around a prem unit, having had six premature babies, but basically they fooled me.

"They fooled me not once but they fooled me twice. I am angry about that.

"They certainly didn't get consent from me. I wasn't asked to sign any consent form or given any written information."

Lisa Brereton's son Joshua died at the hospital in 1991 after undergoing treatment on the experimental ventilator.

Mrs Brereton said she did not remember signing a consent form and alleged she was not told her son was taking part in a medical trial.

She said she was horrified to learn of the experiment.

"I don't remember seeing any form and there wasn't any detailed consultation.

"At the end of the day I'd just been through labour and given birth and was absolutely exhausted.

"How can anyone claim that I was then taken through all the pitfalls and dangers of experimental treatment in that condition? That is madness."

In a statement the hospital said that it is "aware that, and is concerned that, some parents feel they were not fully informed about the study".

But the hospital claims that consent was obtained from all parents whose children took part in the study.

Debbie Henshall claims she was fooled by the hospital

The statement says: "When these concerns were first raised in May 1997, the hospital put on record that it holds the consent forms for this study.

"There is no evidence to support the implication that any disability or death was a consequence of the study."

The Independent newspaper claimed the inquiry is concentrating on whether an experiment at the hospital was allowed to go on too long.

It is also said to address the issue of whether proper consent was obtained from the parents who allowed their babies to take part in the trial.

The trial was carried out by consultant paediatrician Prof David Southall, who has previously attracted controversy over other studies including covert video surveillance of parents suspected of child abuse.

BBC Health Correspondent Richard Hannaford: "So far, the Trust have been saying very little"

The case was brought to the attention of the ministers by Llinn Golding, MP for Newcastle under Lyme, who was approached by the Henshalls a number of years ago.

She had asked then for a government inquiry, but nothing had happened.

She said: "Parents may have known what was going on, but they did not properly understand and this needs to be looked at."

Team of experts

A spokeswoman for the Department of Health said Professor Rod Griffiths, regional director of public health for the NHS Executive West Midlands region, was undertaking the review.

She said he would be conducting "a review of the general framework for both the approval and monitoring of clinical research projects at the hospital".

Prof Griffiths is working on the case with a small team of experts.

All clinical trials have to be first approved by an Ethical Committee made up of science specialists.

The General Medical Council said it had received complaints from parents and was deciding what action to take.

"We are aware of concerns about this research and we are deciding what action to take," she said.

The Continuous Negative Extrathoracic Pressure (CNEP) ventilator used in the trial works in the opposite way to a traditional ventilator, using the same principles as an iron lung.

The usual method of ventilation works on positive pressure, whereby a tube is inserted into the throat before air is forced into the lungs.

A CNEP ventilator works by creating a vacuum around the outside of the chest, making the pressure inside the chest greater than the pressure outside.