Some experts believe that this may be the reason why a number of children died and dozens of others suffered permanent brain damage after being vaccinated in the late 1960s and early 1970s. Last night MPs demanded a full inquiry.

An Observer investigation can reveal that:

• Two batches of Wellcome's whooping cough vaccine, which were more than 14 times more potent than the British standard dose, were given to GPs in Britain and injected into babies;

• 14 other batches containing thousands of vaccine doses were not put through a crucial toxicity test.

One of the toxic batches now known to have been injected into British babies was the same batch that led the Irish Supreme Court in 1992 to award £2.7 million in compensation to Kenneth Best, a Cork boy who suffered permanent brain damage.

At the time the Irish judge accused Wellcome of negligence and attacked the company's poor quality control at its Kent laboratory.

Now, nine years after the award, the Irish Department of Health has received details from Glaxo SmithKline, as it is now known, about the batch - numbered 3741 - and is tracing 296 Irish children who were inoculated with it. Pressure from Denis Naughten, a senior Irish MP, has forced other disclosures from Glaxo SmithKline, including the fact that a second batch of vaccine, numbered 3732, produced by Wellcome around the same time, was even more potent than that used on Best in 1968. In the three years after Wellcome produced the toxic batches, dozens of British parents believed their children suffered brain damage or even died as a result of the whooping cough vaccine.

But their views were dismissed by drug companies and health officials, who insisted the vaccine was safe and important in stamping out a dangerous disease.

Official figures show that reports of adverse reactions during this period soared and a number of babies died hours after receiving their jab.

Gordon Stewart, emeritus professor of public health at Glasgow University, has described the revelations as 'scandalous'. Stewart, who in 1984 was asked by the government's Chief Scientific Officer to investigate a link between brain damage and the vaccine, said he advised the Department of Health about these potential toxic batches in 1989 but they did not act.

His report, which was never published by the government but has been seen by The Observer, is highly critical of the whooping cough vaccine used at this time which he believes was too toxic. Ian Stewart, Labour MP and chair of the all-party Commons committee on vaccine issue, last night said he would be holding an emergency meeting of the committee this week and tabling a series of parliamentary questions. He said: 'The families need to know the truth. If it can be shown that Glaxo Wellcome were negligent in allowing toxic vaccines to be used, then the company must face up to its responsibilities.'

The families of vaccine-damaged children receive £100,000 compensation from the government fund financed by the taxpayer. Stewart believes if the firm is at fault, then they should pay compensation which would be significantly more.

Olivia Price of the Vaccine Victims Support Group said the revelations were 'an utter scandal'. She said: 'These are our children who have had promising lives destroyed. It is now up to the company to give us the information we need.'

A spokesman for Glaxo Smithkline said: 'GSK does not accept that these batches were harmful.'