The family of young man with mental health problems who died after he was left naked on the floor of a police cell have strongly criticised the way their son was treated.

Former public schoolboy James Herbert was detained under the Mental Health Act after being seen acting oddly in a street in Wells, Somerset.

He was restrained by police and placed in the back of patrol van and driven almost 30 miles to Yeovil police station before being carried on a blanket into a cell.

A coroner's jury that heard the case at Wells town hall concluded that Herbert died of cardiac arrest after taking a "legal high".

But it also highlighted factors that may have contributed to his death including a lack of communication between police officers about the man's mental health, his drug use and previous incidents; the failure to call for medical assistance while he was being taken to the police station; and the need for closer monitoring of him.

East Somerset coroner Tony Williams said he would be writing to the chief constable of Avon and Somerset police, Nick Gargan, to highlight the issues raised.

Speaking after the narrative verdict, Herbert's parents, Tony Herbert and Barbara Montgomery, criticised the way the police handled their son's detention.

Mr Herbert said: "On 10 June 2010 at 7pm our son James was in a distressed state running in and out of traffic on the Bath Road in Wells about 400 metres from his home.

"One-and-a-half-hours later he lay dying naked on a bare concrete floor of a police cell at Yeovil police station. The CCTV pictures of our dying son tell it eloquently, the story of catastrophic errors, disregard and neglect shown to James's welfare."

Avon and Somerset police said the case was a "tragedy". Chief Superintendent Nikki Watson said: "This case reinforces the dangers of legal highs. My officers were faced with an extremely difficult situation and did their very best to protect James and other members of the public.

"We have taken note of the coroner's helpful comments about communication, risk-assessment and places of safety."

Deborah Coles, co-director of the campaign group Inquest said: "This is sadly not an isolated case and the issues of concern raised by the jury and coroner are not new. Inquest is working on too many cases of people suffering mental illness who have died after being restrained by police and there is no evidence that any of the collective learning from these cases is being acted upon."