The number of children diagnosed with autism in America is continuing to increase at a rate of more than 20% a year, according to the latest figures published by the US Department of Health.

The figures show that in the year 1999/2000 the number of schoolchildren in America with autism was 65,396 compared with 53,576 the previous year.

Figures have risen steeply since the reporting of autism became mandatory in American schools in 1991. At first the increase was attributed to better reporting of the condition but after nine years some experts argue that the consistent rise must demonstrate an actual rise in autism rates.

The availability of the figures, published has prompted calls from campaigners in Scotland for a national autism register in this country. There is no national register in the UK detailing the number of children affected with the condition. Parents argue that this makes it difficult to provide adequate services and monitor increases.

It is estimated that up to one in 175 primary school children are autistic.

Bill Welsh, chairman of Action Against Autism, said: 'The USA statistics are incontrovertible proof of the autism epidemic which is sweeping the Western world. An epidemic which the health authorities are shamefully trying to cover up.

'A request to the Scottish Executive, made almost two years ago, to establish a register, by year of birth, of autistics, would have confirmed that this tragic condition had gone from rare to common since 1990.'

Dr Ed Yazbak, a retired American paediatrician, insists that the increase is real and argues that this can only be attributed to environmental factors. He says vaccination may not be the only cause but is convinced that it plays a part.

He said: 'These statistics tell us, not only that there has been a huge increase in autism rates in the last 20 years, but also that this increase is not stopping.'

He also argues that the increase cannot just be the result of better diagnosis because the same diagnostic techniques have been used since 1994.

'The criteria for diagnosing children has not changed and the people giving the diagnosis have not changed therefore this must be an increase in numbers and this must be due to environmental factors. We may find that this is being caused by something other than vaccination but it is certainly not genetic because this happens in the second year of life.'

The US has an extensive vaccination programme, with babies given their first vaccine against Hepatitis B in the first two days of life and another two doses before they are 18 months old. Children also have five doses of diphtheria and tetanus, two doses of MMR, four of the Hib, (for meningitis), one of chickenpox, four of the polio vaccine and now four doses of a vaccine to prevent ear infections before they go to school.

'There are definitely too many vaccines,' said Yazbak. 'I don't think it is just vaccines but it is pretty crazy to give vaccines on the first day of life when the child doesn't need.'

Raymond Gallup, president of the Autism Auto-immunity Project, a US campaign group, said: 'I attribute this increase to over-vaccination. There is no doubt about it and MMR is the most problematic one. Children are definitely getting too many vaccines too early in life.'

Last week the Scottish Executive announced that children are to receive a booster shot of whooping cough vaccine in the year before they start school. On Monday the whooping cough vaccine will be added to the combined diphtheria and tetanus booster given to children in their pre-school year.

But Professor David Goldberg, deputy director, the Scottish Centre for Infection and Environmental Health, believes the increase is due to better recording and diagnosis of autism.

He said: 'The increases are likely to be due to greatly improved case ascertainment.'

Massachusetts is known to have had the best health, social and educational provision for autism, of any state in the USA; it has recognised autism for longer than any other state and therefore its figures are likely to be most reliable. Interestingly, the increase in the number of recorded cases in Massachusetts was only 10%.