Jamie King, 39, was found dead at his flat in the city having taken protonitazene, a synthetic painkiller so dangerous it never passed clinical trials.

The drug is sweeping the country and has been blamed for a string of deaths, prompting the authorities in Norfolk to issue an alert.

An inquest into Mr King's death heard he had not been aware of the potency of the drug and may have been sold it in error.

A housemate told the hearing that a man had turned up at Mr King's flat shortly after he was last seen alive and banged on his door shouting "I sold you the wrong s**t".

Jaqueline Lake, senior coroner for Norfolk (Image: Denise Bradley)

Mr King had a long history of illegal drug use and dependence, as well as mixed anxiety and depressive disorder.

His body was found at his sheltered housing accommodation in Marlpit Lane, on June 16.

He had taken a mix of heroin and cocaine but had been unaware the drugs had been cut with protonitazene.

A post mortem examination found he had died of "combined drug toxicity".

His inquest was told he had last been seen by his housemate three days earlier, on June 13, and "seemed fine" as he headed to his room.

But just ten minutes later, another man turned up "asking for Jamie” and headed towards his door.

The housemate said: “I heard the man shouting, ‘Jamie, Jamie, Jamie’ and banging on his door.

“He then shouted, ‘I sold you the wrong s**t'.

"He then smashed his phone on the stairs, and then he took his chip out of the phone, smashed it with his hand and then said, ‘have you got Jamie’s number?’

“I replied ‘no’.

“He then went out of the door into a silver car and drove off.”

The........

© Norwich Evening News