Campaigners say many people are falling through the gaps

The National Autistic Society (NAS) is also calling on ministers to commission a national strategy for adults with autistic spectrum disorders (ASD).

A report published by the NAS has claimed that many ASD sufferers are unable to access advocacy groups to represent them on issues such as finance and housing.

Robert McKay, the national co-ordinator for the NAS in Scotland, said advocacy organisations were "vital" in enabling adults with autism to be more independent.

But he warned that the executive must take steps to make them more widely available.

The situation for children affected by autism is beginning to improve but adults continue to be marginalised or ignored NAS spokesman

He said: "Better resourcing and tailored training and information is needed if advocacy organisations are to adequately support this group of people.

"The NAS believes it is vital that people with autistic spectrum disorders receive the best possible support when they are trying to obtain access to the right services."

More than 500,000 people throughout the UK are thought to have ASD.

But in Scotland, many ASD sufferers are falling through the gaps because the focus is on learning disabilities, not specifically autism, the society says.

"The situation for children affected by autism is beginning to improve but adults continue to be marginalised or ignored," said an NAS spokesman.

Progress is being made in a number of areas Scottish Executive spokeswoman

"The NAS feels that the time is right for needs of adults to be better determined through the creation of a national strategy, similar to the national autism plan for children.

"Commission of such a strategy for adults will indicate the executive's long-term commitment to people affected by autism."

A Scottish Executive spokesperson said it had asked NHS boards and councils to carry out an audit of ASD services.

The findings of that study are now being analysed.

"Progress is being made in a number of areas. For example, in South East Scotland a regional ASD consultancy service has been set up specifically for people over 18 thought to have ASD.