Joseph Benett died after 'inhaling unknown gas'

Joseph Benett died last week after being in a coma for a month

A north London teenager died after inhaling an unknown gas from a canister he thought contained laughing gas, it has emerged.

Joseph Benett, 17, suffered a cardiac arrest after inhaling the gas with his friends on 31 August.

An interim Hertfordshire Coroner's Court report gave the cause of death as hypoxic brain injury caused by inhalation of nitrous oxide.

But police have now said the canister did not contain nitrous oxide.

The teenager, a promising art student from Golders Green, fell into a coma after he inhaled the gas and died at the end of September with his family at his bedside.

The interim inquest was opened and adjourned on 1 October, when the cause of death was given as hypoxic brain injury caused by inhalation of nitrous oxide.

However, Insp Ken Townsend, of Hertfordshire Police, said further investigations had found no trace of nitrous oxide.

"We are still awaiting a full scientific report and, until we receive that report, it would not be appropriate to make any further comment," he said.

"The incident is an immense tragedy. There is currently no criminal investigation and the matter is in the hands of the coroner."

A full inquest is due to be held next year.