The NHS is paying private firms an “eye-watering” £181m a year to look after people with serious mental health problems in units often hundreds of miles from their homes.

A shortage of NHS mental health beds in England means it is being forced to hand companies such as the Priory and Cygnet Health Care larger sums each year, official figures show.

The amount those firms receive to provide residential rehabilitation for those with high-level mental health needs has risen from £158m in 2016-17 to £181m last year – an increase of £23m. Their share of the money spent by NHS clinical commissioning groups (CCGs) on such care has also grown from 54% to 57% over the same period, a British Medical Association (BMA) investigation found.

There is concern that some of the privately run units where patients end up may be providing poor care and a harsh environment, such as that recently seen at Whorlton Hall near Barnard Castle in County Durham, where apparent mistreatment of residents has led to a number of staff facing criminal charges after an undercover exposé by the BBC Panorama programme. Some patients stay for years.

Mental health experts are also worried that the long distances some people have to travel to get a bed heightens their vulnerability and makes them less likely to recover from their illness.

“As seen in the cases of Whorlton Hall and Winterbourne View, the ‘cut-off’ nature of these institutions can be a breeding ground for the development of harsh and abusive cultures. This has no place in modern mental healthcare,” said Dr Andrew Molodynski, an NHS psychiatrist who is the BMA’s lead for mental health.

“As well as the debilitating impact on the patient, the eye-watering sums being spent on out-of-area private providers is a clear sign that the government must get a grip on this worrying practice. There are no positives here for patients, families, care services or the public purse – quite the opposite.”

The BMA’s Doctor magazine used freedom of information laws to find out how often CCGs found a place in the NHS, or had to use a private hospital, for a patient needing mental health rehabilitation in the last three years. However, only 78 of the 176 CCGs that responded gave full data, so the £181m is an underestimate of the true sum paid out.

In all, 18 of the 195 CCGs have no NHS beds available locally and so use only private firms, Doctor discovered. Sandwell and West Birmingham CCG spent the most – £20.26m – over the three years, though Walsall CCG paid £12.5m and East Lancashire CCG handed over £12.44m.

The 2,600 NHS patients sent to private clinics over that period included 140 who faced a round trip of more than seven hours from their homes. One patient from Northamptonshire ended up in a private hospital in Glasgow, while someone from Kent went to a private unit in Darlington.

Among the private providers used by the NHS, Cygnet Health units were used 404 times, Priory facilities 316 times and Cambian Group hospitals 168 times over the same period.