Mencap, the charity for people with learning difficulties, says Nadya Rivera has appealed for leave to stay in the UK on compassionate grounds.

An American citizen, Ms Rivera has been in Britain since 1995, when she came here with her British guardian, Doris Vasquez.

Mrs Vasquez applied for permanent residence for Ms Rivera, but died in 1996 before the process was completed.

She was then put in a private nursing home in Newbury, Berkshire.

In June, the Home Office told Ms Rivera that her application for permanent residence had been rejected.

It said this was because she no longer had relatives in the UK, had a "tenuous" link with Britain and the cost of her care would be high.

It believes the US should pay for her care.

Traumatic

But Mencap argues that it would be "extremely traumatic" for 31-year-old Ms Rivera to be repatriated.

"Mencap Newbury has been working for the last 18 months to keep her in the country," said a Mencap spokeswoman.

"We do not want her to suffer this upheaval. She knows the people around her and can recognise them. We don't want her to experience having to be uprooted."

Autism is a disorder which affects the normal development of the brain.

It causes problems in reasoning, communication skills and social interaction.

Autistic people find it difficult to relate to others, although they may have great skill in retaining lists of facts.

Their difficulty in relating to others means they have problems adapting to change.

Mencap Newbury is acting as Ms Rivera's advocate. It believes she will not be repatriated while her appeal on compassionate grounds is being assessed.

A spokeswoman for Reading Borough Council, which is paying for her care, says it will continue to do so until her appeal is heard.

It has been working with the International Social Services Agency in New York and Ms Rivera's legal representatives on how to return her to the USA.