The founder of a mental health charity has claimed his son became addicted to heroin because of a lack of mental health services in Wandsworth.

Richard Hornsby, who started up the Mond Foundation, said his 26-year-old son turned to the illegal drug when staff refused to help him deal with his mental illness.

South West London and St George’s Mental Health Trust (the trust) has launched an investigation following the accusations.

Mr Hornsby said: “It’s a completely dysfunctional service.

"They don’t have the commitment to caring for patients that they should have.”

His son, who has attention deficit hyperactivity disorder and autistic spectrum disorder, was sectioned at 16 and diagnosed with bipolar disorder at 18.

In 2007, he was ill with side-effects of his anti-psychotic drugs, but his psychiatrist was on holiday for several weeks.

Unable to sleep or sit still, he called the Furzedown community mental health team but claims they refused to see him in his doctor’s absence.

He tried the Crisis Line, a 24-hour home treatment service, but was told he was not eligible for help.

In desperation, he said he accepted some heroin from a friend – which relieved the symptoms.

By the time his doctor came back, he claims he was addicted.

The son, who does not want to be named, said: “If they had treated me and given me the proper drugs I would not have gone through this addiction.”

A trust spokesman said the claims were just allegations at this stage: “We are aware of the concerns raised.

"And although we have addressed previous concerns raised by his family the concerns outlined have not been specifically raised with us as part of a formal complaint.”