Des Browne, the defence secretary, appears to have misled MPs when he told them an independent report had ruled that the RAF's Nimrod aircraft were safe to fly.

Browne made the claim while apologising to relatives of 14 men killed when leaking fuel led to an explosion which destroyed a Nimrod spy plane over Afghanistan in September 2006.

A copy of the independent report, obtained under the Freedom of Information Act, shows that it found the aircraft did not comply with the Ministry of Defence's own safety rules.

The report, produced by QinetiQ in March last year, was highly critical, making 30 recommendations that had to be carried out before the aircraft could be deemed to be safe.

Briefing MPs on the results of the board of inquiry into the loss of the aircraft, Browne insisted the RAF's fleet of Nimrod aircraft were now safe.

"QinetiQ has conducted an independent investigation into the fuel system and confirmed that, in light of the measures taken since the crash, the fuel system is safe to operate," said Browne.

Under the MoD's own rules, for an aircraft to be safe the risk must have been "reduced to a level that is Alarp [as low as reasonably practicable] and broadly acceptable or tolerable".

The QinetiQ report said that only half this condition was in place — while the risk associated with the aircraft was tolerable, "the level of risk present to the fuel system is not Alarp".

The RAF had to take action on its recommendations "before it can be considered that the equipment risks are Alarp".

The QinetiQ report found that during air-to-air refuelling fuel was flowing at twice the speed deemed safe for vital parts of the fuel system. It also showed that a light on the flight engineer's panel that would flash if there was too much pressure in the fuel system had been deliberately disconnected. The report expressed concern that:

- The only safety requirements for the fuel system dated back to 1956 for use with the Nimrod's civilian predecessor, the Comet airliner;

- Nobody in the RAF or the MoD could find a copy of the airworthiness requirements for the version of the aircraft that caught fire; oThe Nimrods had flown nearly twice as many hours as the design requirements laid down as safe;

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