Up to 85 mental health patients per month in south-west London are treated outside their local area due to a shortage of beds.

Figures released in response to a parliamentary question from Labour’s mayoral candidate Sadiq Khan revealed there were 380 people covered by London’s mental health trusts placed in beds outside their area in September 2014, rising to 460 in July 2015.

At South West London and St George’s mental health trust, which covers Sutton, Kingston, Merton, Richmond and Wandsworth, there was an average of 85 patients treated outside their area over the last 10 months.

On at least five occasions in March this year patients had to travel more than 20km for treatment.

A spokesman for the trust said: “We have made 10 additional beds available in 2015 to help ease bed pressures.

“The priority for the NHS is to make sure that when a patient needs to be admitted that they have a bed available.

“On some rare occasions we will secure a patient a bed at another hospital because we are caring for as many people as we have capacity for.

“Evidence shows that people are more likely to recover quicker when they are being treated at home or in a community setting.

“We have been working very closely with our five clinical commissioning groups in south west London who commission our services to review the number of beds that are needed.

“At the same time we are working together to review the investment in our community services which can reduce admission to hospital by almost 50 per cent.”

Mr Khan said: “Everyone knows a family member, friend or work colleague who’s suffered with mental health problems, and the prospect of them receiving treatment a long way from home because of a shortage of specialist beds is very worrying.

“We are once again seeing how support for those with mental health problems has been a Cinderella service and ministers don't seem to be anywhere near getting a grip on the issue.”