Yet the Scottish figure is still lower than that for England and Wales, where the rate is one in 86, and since there are no reasons for a disparity across the UK, it is believed that Scotland is behind in diagnosis . The new figure comes from a survey of Scottish schools by the National Autistic Society.

Robert McKay, national co- ordinator for Scotland at the NAS said: 'Autism is a significant problem for schools and numbers appear to be rising. However, there is an issue over diagnosis and assessment as it would seem we are not picking up the numbers of children we should .

'Nonetheless, with numbers at such a high level, we need the Executive and local authorities to recognise this and take appropriate action to ensure that all children with autism spectrum disorder are given full support to reach their potential.'

The study also found that 89% of schools surveyed are dissatisfied with the extent of their teachers' training in autism. One-third of schools with children with autism have no access to speech and language therapy.

But parents of autistic children last night said they were not surprised by the findings and called for earlier diagnosis and better research into the causes of the condition.

Scott and Jill Guild from Edinburgh have an autistic son, Jack, who they believe developed the condition after receiving the MMR vaccine at 15 months.

'I am not surprised that the statistics are starting to confirm what we thought for a long time -- that there is an increase in the number of autistic children. In my opinion the diagnostic process is not what it should be, it's not made early enough,' Scott said.

David Thrower, also father of an autistic child, added: 'The NAS's finding that there are such high rates of autism amongst mainstream primary-age schoolchildren, quite apart from those autistic children in special schools, should be a wake-up call to health professionals in Scotland. Such a rate is vastly higher than figures previously released. These increases cannot possibly be fully explained by better diagnosis and greater awareness alone.

'Something is clearly going wrong. It is vital that the Medical Research Council commissions urgent clinical research into the children affected, particularly in view of the recent findings by Andrew Wakefield, John O'Leary, Vijendra Singh and others suggesting a link with the MMR vaccine. We have to find out what is damaging these children, notably those who acquired autism later in their childhood.'

The figures have prompted renewed calls for the Scottish Executive to revise its immunisation policy. Nicola Sturgeon, shadow health minister, said: 'The figures are alarming. This underlines the need for more research into the causes of autism and undermines public confidence in the MMR vaccine. The current government policy of refusing to offer single vaccines threatens to further reduce vaccination uptake which will present increasing danger to children.'

Mary Scanlon, Conservative health spokeswoman, who is also calling for single vaccines to be made available as an alternative to the MMR vaccine, added: 'The main point is that autism figures are increasing and continuing to increase at an alarming rate. It is time that we made serious efforts to find out the causes of autism.'

Last month an expert group set up by the Scottish Executive ruled that there should be no change to the vaccination policy to allow parents concerned about the MMR jag to request single vaccines for their children. A Scottish Executive health spokeswoman said: 'This is an interesting, if small, questionnaire study of 169 schools in two authorities in Scotland. A number of the points raised in the report are already being taken forward by the Executive.

'Ministers have already announced that they are providing almost £700,000 through a grant programme to improve services for children with autism and their families. Included within this is funding to the NAS to improve training for professionals working in the field of autism spectrum disorders.'

National Autistic Society helpline: 0870 600 8585