A dad-of-two was prescribed a fatal dose of medication following "multiple failures" by staff at mental health hospital, a jury has found.

Derek Richards, 39, of Selhurst, died of an overdose of methadone and diazepam while being treated at Bethlem Royal Hospital's psychiatric intensive care unit in 2012.

A four-day jury inquest at South London Coroner's Court concluded last week "systematic failures in training and procedure" had led to his death.

Mr Richards, who had a long history of mental health problems and drug use, was arrested and sectioned in April 2012 and transferred to the Beckenham hospital, run by South London and Maudsley (SLAM) NHS Foundation Trust.

At the hospital, he was prescribed methadone to manage his drug dependency but repeatedly asked for his dosage to be reduced in the month before his death.

The inquest heard Mr Richards refused his methadone during three separate periods, lasting a total of nine days, and on a fourth occasion had his dosage lowered because the ward had run out of the drug.

But clinical staff failed to take into consideration that these periods off the methadone would lower his tolerance for the drug and did not adjust his dosages.

A toxicologist told the inquest the levels of methadone and diazepam found in Mr Richards' blood following his death in May 19 were consistent with those prescribed and administered to him by hospital staff.

The inquest also heard paramedics called to treat Mr Richards were left to drive around the hospital site for seven minutes because there were no staff to direct them to his ward.

Clair Hilder, the solicitor who represented Mr Richards' family at his inquest, said: "When Mr Richards went to Bethlem Royal Hospital his family thought that it was the best place for him and that he would be safe there.

"In fact, as the jury made clear, the hospital did not have adequate training in place for staff, nor were there sufficient systems in place to safeguard those who were prescribed powerful medication."

The jury found methadone and diazepam toxicity to be cause of his death and recorded a conclusion of accidental death due to systematic failures in training and procedure.

In a damning verdict, they highlighted "inadequate training" at the hospital in drug charts, nursing and the risks of methadone and diazepam, as well as a lack of communication between nurses, pharmaceutical staff and doctors.

The jury also concluded staff failures to keep adequate records had contributed to Mr Richards' death.

After the inquest, his aunt Linda Simmons said: "It is now almost three years since Derek's death and I am pleased that the failings which occurred at the hospital are now out in the open.

"I hope that this will help ensure that this does not happen to anyone else in the future.

"Whilst many changes have been made I am still concerned that the hospital's drug prescription and administration charts are kept separately from patient's medical records, so that missed doses may not always be clear."

A spokeswoman for SLAM said: "The trust acknowledges the sad death of Derek Richards who was an inpatient at Bethlem Royal Hospital in May 2012. We offer our sincere condolences to his family.

"The trust has carried out a full and robust investigation following his death and has identified lessons that we can learn.

"The trust co-operated fully with the coroner’s inquest and shall be providing the coroner with further assurances about changes which have taken place within the trust over the past two years."