It could be the health care crisis that never was. The perception, over the last two decades or more, that autism was on the increase led to a desperate search for the cause.

In Britain that led to widespread fears of a link with the MMR vaccine for measles mumps and rubella.

But new research published today suggests that the huge increase in reported cases of autism since 1979 may simply be a result of more awareness, more knowledge and better record keeping.

Richard Watson reported.

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RICHARD WATSON:
Four-year-old Thomas Ziegel suffers from seriously delayed speech. When he and his twin brother Benjamin were toddlers their mum noticed some minor repetitive behaviour. They were both diagnosed on the autistic spectrum last year.

SARAH ZIEGEL:
Thomas used to do strange things with toys. We asked what that was and everyone said don't worry. Finally just threw at us one day, oh, might be autism. We will see you in six months. That was the attitude. We then panicked and thought it wasn't anything we had ever considered. We never thought they were autistic because they are friendly, happy little children.

RICHARD WATSON:
The cases of Benjamin and Thomas Ziegel go to the heart of the current controversy surrounding the incidents of autism across the world. Some researchers including those behind today's report, argue a decade ago they may well have been categorised as developmentally delayed rather than autistic. Today's report is based on medical records of 186,000 children living in North East London. The authors say the incidents of autistic spectrum disorders rose from 1979 to 1992. But the figure levelled off to 45 to 50 new cases per year. Thomas and Benjamin are given intensive therapy to try to fully connect them with the outside world. The researchers argue if there was an outside factor at play such as the MMR jab, you would see numbers continuing to rise. Parents are angry alleging it is simply a vehicle to discredit the author's colleague. That is strongly denied.

PROFESSOR BRENT TAYLOR:
I'm interested in good science and our paper is good science. Part of the scientific method is see if you can confirm your hypothesis.

RICHARD WATSON:
Beyond the narrow debate over MMR there are still scientific disputes about the prevalence of autism. Much of the new thinking comes from the United States. Californian state researchers say cases of the most serious or classical autism were steady during the 1970s at around 200 cases per year, but in the mid-1980s the numbers began to climb. Today the total number has reached more than 20,000; It has doubled in the past four years alone. Those with autism now account for 40% of the state's entire special needs caseload.

RON HUFF:
A portion of the rise can be attributed to a change in the way we interpret and use the criteria for diagnosing kids. We don't believe at this point that it could be 100% attributable to that shift in the diagnostic criteria. We suspect there could be other factors contributing to the increase and we're putting our energy into trying to determine what that is.

RICHARD WATSON:
The Californian state is funding a huge study to examine whether environmental factors can be linked to autism while Britain still debates whether there is any rise in case loads at all. Studies of twins where only one is autistic proves that environmental factors can have some impact, perhaps even in the womb. Other studies show a higher prevalence of autism in children of parents who've contracted rubella, or in the 1960s used the drug thalidomide.

DR IRVA HERTZ-PICCIOTTO:
This is the first comprehensive examination of environmental factors in autism. We are the first group to take on a broad range of chemicals including medications, PBDEs, metals, pesticides, household products, chemicals that are in personal care products, to see if they may play a role in the development of autism.

RICHARD WATSON:
But the American research suggesting that outside factors may be at play is rejected by the author of the British study.

PROFESSOR BRENT TAYLOR:
The evidence is that it's got the highest genetic load of virtually any developmental problem, at least 80%. I'm sure that the evidence is that most of it originates and is evident from very early in gestation in the womb.

RICHARD WATSON:
So 80% is not ruling out the importance of some environmental factors?

PROFESSOR BRENT TAYLOR:
There must be some triggers that do it. I think these are either inter-uterine or early in life. The evidence that any external force, like the MMR vaccine after the first birthday might trigger autism, there is nothing to support it.

RICHARD WATSON:
Many parents don't agree. More cases are certainly being diagnosed. In a recent survey, 87% of Local Education Authorities reported an increase in autism cases. Putting pressure on funding. The Ziegel family had to pay for eight months of intensive treatment on their own. Around £30,000 when their London council, Richmond, refused to pay.

SARAH ZIEGEL:
Our local authority doesn't want to fund. They just ignored it. Our only option was to go to tribunal special education needs tribunal which we did at the beginning of the year. That is a stressful experience and very expensive. We did go and it was worth while and we did win full funding for 35 hours a week, which we finally got a few months later.

RICHARD WATSON:
More and more local authorities are refusing to fund intensive therapy which is why reports about rising case loads are still politically hot. Today's report suggests that 1 child in 364 is being diagnosed with autism in the north east London sample That's much lower than the estimate from the Medical Research Council of 1 in 167 and lower than the estimate from the National Autistic Society of 1 in 86. Today's report will offer some comfort to the Government which has been keen to back MMR, but as new thinking emerges from California, many British parents will press for more research here.

This transcript was produced from the teletext subtitles that are generated live for Newsnight. It has been checked against the programme as broadcast, however Newsnight can accept no responsibility for any factual inaccuracies. We will be happy to correct serious errors.