A group of scientists in America said it had found a strong association between the vaccine and an autoimmune reaction thought to play a role in causing the developmental disorder.

However Peter Lachmann, Emeritus Professor of Immunology at Cambridge, said that the conclusions drawn by Vijendra Singh and his team did not make for a direct link between MMR and autism.

“In my view the associations that Dr Singh makes do not follow. His hypothesis does not show causality; he is drawing unjustifiable conclusions from the antibody data he has collected. I do not think such conclusions can be drawn.”

Groups campaigning against the MMR vaccine last night welcomed the findings and called for further independent research into a possible link between the vaccine and autism.

The scientists based at Utah State University in Logan analysed blood samples from 125 autistic children and 92 children who did not have autism. Of the autistic cases, 75 were found to suffer an unusual reaction to the measles component of the MMR vaccine, which was not recorded in the normal children.

The researchers, led by Professor Singh, found a “significant increase” in the level of MMR antibodies in the autistic cases. Nine out of ten autistic samples which showed an immune response to MMR were also positive for antibodies thought to be involved in autism.

Uptake of the MMR vaccine in the UK has dropped in recent months amid heightened fears that it might trigger autism. More than 2,000 families here have taken legal action, claiming their children have been damaged by the jab, but health officials continue to insist that the scientific evidence shows MMR to be the safest way to protect against measles, mumps and rubella.

According to the latest US evidence the antibodies generated in reaction to the MMR jab attack the brain by targeting the basic building blocks of myelin, the insulating sheath that covers nerve fibres.

The scientists, who report their findings in the latest issue of the Journal of Biomedical Science, concluded: “Stemming from this evidence, we suggest that an inappropriate antibody response to MMR, specifically the measles component thereof, might be related to pathogenesis of autism.”

MMR vaccine uptake in this country for 16-month-old children dropped from 76.2 per cent to 72 per cent between December and April. Immunisation for 24-month-old children fell from 85.8 per cent to 84.4 per cent over the same winter period and then increased to 85.9 per cent.

Both sets of figures fall far short of the Government’s target of 95 per cent.