By Alex Stevenson
The government will be pressured to end its "unfair and wasteful" treatment of those with autism at a conference in London today.
Conservative leader David Cameron will address the conference as it seeks to explore why adults with autism are frequently let down by society.
Autism affects around one in every 100 people in the UK, or about 540,000 people. According to a recent National Audit Office report only 15 per cent of these people were in employment.
"We may not know the exact causes of autism; but there is an essential need for better coordinated and informed responses across the lifespan; the starting point for this has to be research," charity Research Autism's chairman Geoffrey Mardell said.
"We hope today's conference allows the government to start work to resolve this unfair and wasteful situation for adults with autism."
Many adults with autism are "totally unaccounted for", the charity says, leading to poor and inappropriate support.
Only two local authorities in England are aware of how many adults in their area are autistic.
And roughly two-thirds of councils do not know how many of the children they are responsible for have autism.
A private member's bill championed by shadow Wales secretary Cheryl Gillan has passed the Commons and is now being scrutinised by the Lords.
It presents the biggest opportunity for change and, if passed by parliament, would become the first condition-specific Act of parliament.
"Our local authorities have no idea what the numbers are - you expect the services to be joined up," Ms Gillan told politics.co.uk earlier this year.
"It's not rocket science - but it's not happening at the moment and it needs to."