The coffins of some of the 14 servicemen killed

The serviceman based at RAF Kinloss, Moray, said a hole in a heating pipe damaged cables, metal and the seal around fuel tanks.

A fuel leak is thought to have been responsible for a Nimrod crash which killed 14 servicemen last September.

The RAF has insisted that Nimrod safety has never been compromised.

The whistleblower, whose identity has been protected, told the BBC's Panorama that the incident on a routine flight from Kinloss came close to a disaster.

He said: "Basically, a hole had developed in one of the heating pipes and superheated air was blasting against the airframe and it burnt through cabling and metal.

He was always saying that there was going to be an accident, a serious one Laura Robson Partner of Flt Lt Steve Swarbrick Fresh fears over Nimrod safety

"The seal around the fuel tanks was damaged as well and that is really serious.

"Chances are, if they'd flown for a few hours more, we may have lost them."

He believed the 14 servicemen who were killed when their Nimrod came down near Kandahar, Afghanistan, would still be alive if new aircraft - already six years late - had been in service.

Laura Robson, from Inverness, whose partner Flt Lt Steven Swarbrick, was one of those who died, told Panorama of his concerns for the safety of the ageing aircraft.

She said: "He was always complaining about the fact that the flights were always delayed because there was maintenance issues.

"He was always saying that there was going to be an accident, a serious one."

Panorama has also uncovered details of two other incidents that happened on board Nimrods in the months after the crash.

Former RAF engineer Jimmy Jones said there was a fuel leak in the bomb bay of one plane.

Asked how serious he considered that to have been, he said: "Well that could have been as serious as the one we lost in September."

PREVIOUS NIMROD LOSSES 17 November 1980: Bird strike at Roseisle Forest, near Kinloss, Scotland 3 June 1984: Fire on board at St Mawgan, Cornwall 16 May 1995: Engine fire at Lossiemouth, Scotland 2 September 1995: Crash at Toronto Air Show, Canada

The results of an RAF board of inquiry into the Afghanistan crash are expected later this year.

However, Moray SNP MP Angus Robertson said the issues he said were affecting the Nimrod fleet had "directly touched" on the families who lost loved ones in last September's incident.

He added: "The MoD has a huge challenge to restore confidence, moral and trust in their management of the Nimrod fleet as it approaches replacement."

The 12 RAF personnel killed were Flt Lt Steven Johnson, Flt Lt Leigh Anthony Mitchelmore, Flt Lt Gareth Rodney Nicholas, Flt Lt Allan James Squires, Flt Lt Steven Swarbrick, Flt Sgt Gary Wayne Andrews, Flt Sgt Stephen Beattie, Flt Sgt Gerard Martin Bell and Flt Sgt Adrian Davies, Sgt Benjamin James Knight, Sgt John Joseph Langton and Sgt Gary Paul Quilliam.

L/Cpl Oliver Simon Dicketts from the Parachute Regiment and Royal Marine Joseph David Windall also perished.

The aircraft had been supporting a major offensive, in which Nato said more than 200 Taleban have been killed.