A "lost generation" of adults is living with undiagnosed autism, according to research.

University of Leicester psychiatry professor Terry Brugha, who led the study, believes many people could be suffering without knowing they have the condition.

Researchers found that nearly one per cent of people over the age of 16 have autism-spectrum disorders, which range from mild Asperger's syndrome to more severe forms of the condition.

Prof Brugha, who is also a consultant psychiatrist at Leicestershire Partnership NHS Trust, said: "Recognition and diagnosis of autism in adulthood is a huge issue.

"Many local authorities have no centralised information and many adults, particularly those with less severe autism, could be leading quite difficult lives with little help.

"There is a lost generation of adults. Most will have seen a GP from time to time but they have not been diagnosed.

"As people hear more about autism we are beginning to hear comments that some patients may have the condition, but at the moment it is anecdotal."

Prof Brugha's study, published in the journal Archives of General Psychiatry, is the first to give an estimate of autism rates among adults in the community.

He said: "We really need to reach adults that are not diagnosed.

"Some will have been cut off from their families because they are seen as 'difficult'.

"To find there is now a medical explanation for that person's behaviour could be a really positive thing.

"We are extending our study to survey those living in institutions and people on disability registers in Leicestershire, Sheffield and south London."

Prof Brugha said he hoped the study would help to improve the recognition and diagnosis of autism and attract more funding for research into the condition, its causes and treatment.

Paul Sandford, from Loughborough, was 42 when he was diagnosed with Asperger's syndrome.

He learnt about the condition while he was working as a further education support worker and realised he had some of the symptoms.

His GP referred him to Prof Brugha, who confirmed the diagnosis.

Mr Sandford said: "It has been a real positive for me.

"It has made me much more aware that people have a different outlook to me.

"As a younger man I would have a lot of arguments with other people and think they were disagreeing with me to be argumentative.

"I did find it difficult socially and only had one or two friends at a time.

"I was very poor at reading people's motives."