Some experts believe that these Trivax vaccines - which had not passed critical company safety tests - may have caused permanent brain damage and even fatalities in young children.

In 1992, the family of an Irish boy, Kenneth Best, who suffered brain damage from one of these toxic vaccines, was awarded £2.7 million in compensation by the Irish Supreme Court.

Despite a long and fierce battle with the drug giant, the boy's family finally won this historic case after his mother Margaret made a startling find when sifting through tens of thousands of company documents.

She discovered that the Trivax vaccine used on her son, from a batch numbered 3,741, had been released by the company despite it having failed to pass a critical safety test. Documents revealed that the 60,000 individual doses within this batch were known to be 14 times more potent than normal.

At the time the Irish judge accused GlaxoSmithKline - then known as Glaxo Wellcome - of negligence and attacked the company's poor quality control at its Kent laboratory. Immunology experts condemned Glaxo in court for what one US scientist described as an 'extraordinary event'.

Last year an investigation by The Observer found evidence to suggest that vaccines from this faulty batch, which may have wrecked Kenneth Best's life, had also been used in Britain.

Liberal Democrat MP Norman Baker raised questions in the House of Commons, asking whether vaccines from this batch had been given to British babies. Then Health Minister Yvette Cooper wrote to the company asking for information.

Now, almost a year later, GlaxoSmithKline has replied that it is 'highly probable' the toxic batches had been used in Britain.

The Department of Health is under pressure to make efforts to trace the children who received the suspect vaccines.

Last week in the House of Commons, Health Minister Hazel Blears said: 'Unfortunately they no longer have details of the quantitites of vaccine or the places where the vaccine was supplied.

'Since vaccines were not centrally purchased and distributed at that time there are no central records either. Information on individuals who received these vaccines will only exist if the general practioner at the time of the immunisation recorded the batch number and the patient's notes are still available.'

Baker will now write to the Minister to demand that she asks health authorities to check the records to find out who received the vaccine. It is believed that at least one boy from Wales died after receiving a jab from toxic batch 3,741, although the parents have never been informed.