A SPY plane which crashed in Afghanistan killing 14 servicemen should not have been passed safe to fly due to a "fundamental flaw" in the aircraft fleet's design, an inquest heard.

A senior RAF officer admitted mistakes were made during a hazard assessment which could have identified the fault that caused the explosion which downed the ageing Nimrod plane.

Air Commodore George Baber said had they known then what they knew now the Nimrod fleet would not have been deemed airworthy.

The hearing at Oxford Coroner's Court had previously been told the tragedy was caused by fuel leaking into a dry bay and igniting on contact with a hot air pipe.

The Air Commodore said having fuel couplings in the same compartment as a hot air pipe was a "fundamental design flaw".

The 37-year-old Nimrod exploded just minutes after undergoing air-to-air refuelling near Kandahar in 2006.

Air Commodore Baber told the inquest that he led a Integrated Project Team, who together with BAE systems, carried out a comprehensive analysis of the Nimrod plane before the crash.

He said a number of hazards were identified and put into categories. He said the possibility of the explosion in the dry bay was graded as "improbable" - one of the lower categories.

But he admitted it should have graded higher which would have then warranted further action.