Image copyright iStock

Deaths linked to a commonly prescribed class of drug, used to treat anxiety and insomnia, reached record levels in England and Wales last year.

There were 372 fatalities involving benzodiazepines, up 8% on the previous year, and the highest level since records began in 1993, according to the Office for National Statistics.

There were more than 10 million prescriptions for benzodiazepines dispensed in England in 2014, but there are growing concerns about the illegal supply of the drugs.

And research for the BBC's 5 live Investigates programme found websites openly offering a range of branded pills without a prescription or oversight from a qualified doctor.

The Home Office said the Advisory Council on the Misuse of Drugs has been commissioned to look into the issues surrounding the illicit supply of the medicines.

And in a statement, the Home Office added that there had been a "long-term downward trend in drug use over the last decade".

Image caption Jason Houghton bought tablets from online retailers

Keith Houghton's son Jason, 24, died in 2014 after he started taking benzodiazepines to help him sleep while working irregular shift patterns as a paramedic.

"He told us that he'd started working nights, which involved four night shifts in a row and then four days," says Keith.

"He was having difficulty getting back to sleep, he was that wired up."

Jason was able to source the drug himself online and quickly became addicted.

"It was clear from the get-go that he was buying them from online retailers which were based abroad," says Keith.

"There were some in Romania. There was one in Germany, another in Pakistan and he was basically ordering them from his home bedroom and getting them delivered by Royal Mail.

"We were so shocked, as any parent would be, that this was so available to anyone.

"If you've got a credit card and access to the internet you can order these kind of drugs straight to your home."

Manchester West coroner Alan Walsh recorded a verdict of death by misadventure because of the combined effects of diazepam and other medicines in Jason's system.

Image copyright Science Photo Library Image caption Benzodiazepines can be prescribed for sleep disorders

Manchester West coroner Alan Walsh recorded a verdict of death by misadventure because of the combined effects of diazepam and other medicines in Jason's system.

He called on Home Secretary Theresa May to take "urgent action" into the supply of benzodiazepines and other drugs online to prevent further deaths.

The coroner also highlighted concerns over one particular online retailer which had supplied several drugs to Jason in padded envelopes through the post.

In response, after an appeal by the Home Office, the medicines regulator the Medicines and Health products Regulatory Agency (MHRA) was able to close down the site.

However, 5 live Investigates has established that a retailer operating under a similar name is currently offering to supply benzodiazepines and other medication. The website is offering 10mg branded benzodiazepine pills in packets of 1,000. It says it will deliver to any UK address within three to five days.

The MHRA said that websites reported to be suspected of operating illegally are investigated thoroughly and appropriate action is taken.

The retailer did not respond to requests for comment about Jason Houghton's death or its online activities.

Research published in The British Journal of Psychiatry in 2014 questioned 1,500 members of the general public about their use of benzodiazepines and so called "Z drugs" used to treat insomnia.

A total of 30% had misused one or more of these medications and 27% of these reported obtaining the drugs via the internet, while a further 11% bought them from abroad.

According to figures from the Health and Social Care Information Centre, in 2014/15 nearly 18,000 people received hospital treatment for drug poisoning linked to benzodiazepines in England, while 584 children under the age of 18 were also treated.

Lady Rhona Bradley, chief executive of the substance addiction charity Addiction Dependency Solutions, said: "Addiction to prescription drugs is a hugely underestimated issue in the UK - estimates believe there could be more than one million people addicted to such prescribed medication as benzodiazepines.

"We need targeted treatment services, separate from mainstream alcohol and drug services.

"The biggest worry for us is that those who have become involuntarily addicted, become so reliant and desperate due to the lack of support, services and advice, that they turn to the internet to supplement their addiction."

Benzodiazepines are subject to legal restrictions in the UK both under medicines regulation and by the Home Office under the Misuse of Drugs Act.

However, considerable activity takes place online, outside UK jurisdiction.

A Home Office statement said: "Our approach to drugs is working and there has been a long-term downward trend in drug use over the last decade. We continue, however, to be concerned about the harms caused by drug misuse, including in relation to prescription-only medicines.

"That's why we continue to control a number of prescription-only medicines under the Misuse of Drugs Act 1971. These include benzodiazepines, tramadol, morphine, codeine and diazepam, and we have commissioned the Advisory Council on the Misuse of Drugs (ACMD) to look into the issues around the diversion and illicit supply of these medicines."

5 live Investigates is on BBC 5 live on Sunday 20 December at 11:00 GMT. You can listen online afterwards or download the programme podcast.