Almost twice as many children in Britain could have autism than previously thought, researchers say.
A study has found that as many as one in 58 may have some form of the condition - well above the widely-accepted existing estimate of one in 100.
If so, it would mean that around 210,000 children under 16 in the UK have autism or a related disorder.
The leader of the Cambridge University study, autism expert Professor Simon Baron-Cohen, said the higher figure was not linked to use of the controversial MMR jab.
However, two members of his team are understood to privately believe that the triple vaccination may be to blame for the rise.
Their fears follow claims from experts that injecting children with the combined measles, mumps and rubella vaccine - rather than three separate jabs - can cause autism.
Autism is an umbrella term for a range of developmental disorders that have a lifelong effect on the ability to interact socially and communicate.
There are related problems, known as autism spectrum disorders, which include Asperger's syndrome, which also require special teaching needs.
Estimates of the number of children with autism have been edging up for more than a decade. In the 1990s, it was believed there were around four or five cases of autism in every 10,000 people - rising to 20 cases if other ASD problems were included.
Later this was revised upwards to one in 100, the widely-accepted estimate among British scientists.
Last year a study suggested the figure may be as high as one in 86, and now the Cambridge team say it could be as high as one in 58.
It is not known whether the rise is down to better diagnosis of the condition, or because the numbers with autism are actually rising.
Professor Baron-Cohen and his team arrived at their estimate by studying the incidence of autism and ASD among 12,000 children at Cambridgeshire primary schools between 2001 and 2004.
He said possible factors behind the rise were genetics, environmental factors such as greater use of pesticides and children's exposure to hormones such as testosterone in the womb.
He said: "As for MMR, at this point one can conclude that evidence does not support the idea that the MMR causes autism."
However, two of the seven-strong team - Dr Fiona Scott and Dr Carol Stott - said the jab, which is given at 12 or 15 months, could be a factor in small numbers of children.
The MMR scare began in 1998 when Dr Andrew Wakefield, a gastroenterologist at the Royal Free Hospital in North London, wrote an article in The Lancet which linked the jab to autism and inflammatory bowel disease.
Despite further research debunking the claims, some mothers opted to go private and pay for three separate jabs or missed the jab altogether.
This month Dr Wakefield could be struck off the medical register following a General Medical Council hearing-over claims of dishonesty and irresponsibility over the research.
Ivan Corea, head of the Autism Awareness Campaign UK, said he hoped the increased estimate would prompt the Government to improve services because autistic people were at the mercy of a 'postcode lottery'.
He said: "We are urging Gordon Brown to provide a world-class education for all children with autism, to provide new specialist autism schools, even special needs academies and autism units equipped with sensory rooms in mainstream primary and secondary schools." (Daily Mail