Ten offshore workers had to be rescued from a normally unattended platform off the Norfolk coast following a gas leak.

The platform, owned by offshore energy company Perenco, had to be shut down to evacuate the crew and has yet to resume work.

A report from the health and safety executive into the incident on June 16 said the crew members, who arrived at the Davy 49/30A platform by helicopter, were "exposed to a risk of serious personal injury from asphyxiation from high concentrations in air of un-ignited gas", as well as the risk of fire or even an explosion had the gas ignited.

It concluded the arrangements and equipment for emergency response "did not provide sufficient protection for personnel on the installation during a foreseeable major incident" and that the response protocol would not be effective in the event of a repeat incident.

Perenco confirmed no one had been injured during the incident.

The report said the location of the gas leak blocked the platform's designated escape route, at the same time preventing the team from escaping by boat or accessing any protective equipment such as life jackets.

Rescuing the crew by helicopter was also deemed too dangerous due to the possibility of the gas igniting.

With the hydrocarbon gas cloud rendering their main escape route impassable, the crew had to gather in an unprotected area below the helideck.

In order to facilitate their evacuation an emergency shutdown of the platform was performed - but this cut power to the fire and gas panel, leaving the on-scene commander with no oversight of gas, heat and smoke detection on the deck, the report said.

The same loss of power knocked out the principal means of communication between the team and the control room at Bacton gas terminal, leaving only hand-held very high-frequency (VHF) radios with a limited range.

The report said this "prevented the clear and accurate communication" necessary to coordinate an "effective emergency response".

A spokesman for Perenco said: "Perenco confirms that there was a gas release on the Davy platform.

"The correct response procedures were followed, which included an emergency shutdown of the platform and notifying the health and safety executive.

"There were no injuries to personnel or damage to equipment. Throughout the incident, the crew was supported by a safety standby vessel.

"An investigation into the cause of the release was subsequently launched and is ongoing."

Perenco, which operates from the Bacton gas terminal and has a base in Norwich, acquired its Southern North Sea assets from BP in 2003.