British scientists have uncovered new evidence suggesting a link between the MMR vaccine and chronic illness in children, including autism.

Their research, presented to the US congress last Thursday, points to the presence of the measles virus in the gut of 24 out of 25 autistic children.

The virus is one of the elements in the combined mumps, measles and rubella vaccine routinely administered to hundreds of thousands of children in the UK.

Congressmen were told that there was "compelling evidence" of an association between infection by the measle virus and autism in the children, many of whom appeared to have developed the condition after they had been injected with the triple vaccine.

The claims come from Professor John O'Leary, the director of pathology at the Coombe Women's Hospital in Dublin, and Dr Andrew Wakefield, who works at the Royal Free Hospital in London.

The initial research was conducted by Dr Wakefield, a senior lecturer in paediatric gastroenterology and the leading exponent of the theory.

His work was then thoroughly checked by Professor O'leary, a leading pathologist, who found himself in agreement with the thesis. A second independent researcher in Japan who has checked Dr Wakefield's work concurred.

The findings will reignite a long-running controversy surrounding the MMR vaccine. Many parents claim that the injection has damaged their children irreparably.

Dr Wakefield caused uproar two years ago when he described in the medical journal, The Lancet, how he had discovered a pattern of inflammation of the bowel, which he believed was part of a new disease, "autistic enterocolitis", in 12 children. He said he had no direct evidence of a link but argued that further investigation was required.

Britain's Medical Research Council claimed only last week that there was definitely no link between the vaccine and either the bowel disorder Crohn's disease or autism.

The American hearing, which took place before the US senate's congressional oversight committee in Washington, is expected to shape US vaccine policy.

A large number of leading US doctors and scientists were in attendance.

Dr Wakefield said the syndrome he has discovered would be described in an authoritative, peer-reviewed medical journal later this year.

He believes there is a strong possibility that the MMR vaccine has led to gut infection and impaired metabolism and liver function, which, in turn, affected the brain in many children with autism or related conditions. He is calling for further research on his "testable hypothesis".

Tests on children with brain function problems - including autism, Asperger's Syndrome and attention deficit disorder - showed that the children exhibited a range of bowel symptoms including pain, constipation and diarrhoea.

Colitis, a close relative of Crohn's disease, and other disorders, were also found.

"I am not anti-vaccine,'' he said. "Rather I want to advocate the safest strategies of vaccination.''

A spokesperson for the Department of Health warned: "The research has not been verified by anyone else, by the normal research methods, including independent experts and as it stands is uninterpretable. This research does not prove anything and there remains no evidence to suggest there is any link between the MMR jab and autism.

MMR was launched in the UK in 1988 and is now given to children at 15 months and again before starting school. Many parents in Britain have responded to the controversy by demanding individual injections for their youngsters instead of the triple jab.