UP to a million under-fives have been inoculated against the flu virus with a controversial vaccine containing poisonous mercury.
Pandemrix has been given to almost a quarter of all healthy babies and young children as well as thousands of older children with health problems.
Inquiries by the Sunday Express reveal it contains a preservative made with a form of mercury that was phased out of childhood vaccines in 2004 after fears about its safety.
The preservative, called thimerosal, has been linked with autism and developmental disorders in children and was withdrawn from childhood vaccines in the United States and parts of Europe 10 years ago.
Yet the UK government has always insisted there is no persuasive evidence it poses a health risk. When it was withdrawn, Labour health minister Rosie Winterton said the move was part of "a global goal to minimise environmental exposure to mercury".
However, many experts disagree. Dr Richard Halvorsen, author of the book, The Truth About Vaccines, said: "Thimerosal is an extremely toxic substance and known poison to the brain.
"There is enough convincing evidence linking thimerosal with developmental disorders and learning problems in individual children to warrant its removal from any childhood vaccine.
"It is irresponsible to administer a jab with little proven benefit which contains potentially harmful toxic substances."