Matthew Poulter, who has autism, was 15 months old when he was vaccinated with MMR. His mother Rochelle, from Brighton, said: 'He had been a sociable child but his speech just stopped. He was not saying anything, just grunts and moans. I am convinced it was the MMR.' Matthew and another child, Robert Miles, have been granted legal aid to sue the manufacturer of the vaccine. Theirs are among 300 cases being handled by Richard Barr, a partner at Norfolk solicitors Dawbarns.

Health managers have been urged to reassure the public after research linking the measles, mumps, rubella (MMR) vaccine to the development of autism.

A study published last week indicates the discovery of a syndrome linking intestinal inflammation with autistic disorder.

Twelve children were referred to specialists at London's Royal Free Hospital because of co-existent behavioural and intestinal symptoms. Parents said the onset of behavioural symptoms followed either an MMR vaccination or a measles infection.

'Given our own observations and previous American research,' the specialists said, 'we are concerned that MMR may give rise to this complication in a small number of children.'

Arie Zuckerman, dean of the hospital's school of medicine, warned the findings might provoke a scare. 'Immunisation programmes have saved countless numbers of children from death and disability.

'Side-effects are uncommon, and rarely severe. The uptake of immunisation fell 1 per cent between April and June last year immediately following media reports that MMR caused Crohn's disease. That's 2,000 children who were not vaccinated.'