Revealed: secret report on Britain's 'rusty' spy planes

Serious safety concerns have emerged over Britain's ageing fleet of Nimrod spy planes – currently patrolling Iraq and Afghanistan – after an investigation by The Independent on Sunday found their fuselages could be riddled with rust.

Sources have revealed that severe corrosion has been found on the 40-year-old fuselages now being revamped in the UK to form the next generation of aircraft. That £3bn project is seven years behind schedule and millions of pounds over budget.

The Government decided in 1996 that the new generation of Nimrods should use the fuselages of the old aircraft. Several were taken out of service and stripped back to the fuselage, and new wings, undercarriage and floors were bolted on. Problems found in the revamped fuselages are likely to be found in the planes still flying because the craft are the same age.

In January 2006 BAe Systems, which is building the new aircraft, discovered cracks in the rivets holding fuselage sections together. In repairing this problem the fuselage skin beneath the rivets has been found to be corroded. As a result, all Nimrod aircraft now in use will have to be checked.

Graham Knight, whose son Ben, 25, was one of 14 killed when a Nimrod crashed in Afghanistan last year, and who has since investigated the aircraft, said: "If rust on aluminium goes undetected it turns into a powder. The thickness of the metal becomes less and less until it can't sustain the stress of flying any more."

The cause of last year's crash remains a mystery, but it is not thought to have resulted from enemy fire.

David Learmount, a former RAF pilot and safety editor of Flight International magazine, said that corrosion was an issue for all aircraft. Nimrods were especially susceptible as they spend most of their lives flying over the sea.

Mr Learmount said: "The strength of the fuselage is severely impaired by areas of jointing that have become weakened by corrosion. A tube of cardboard is strong. But if you cut the cardboard and stress it, you know where it's going to break."

Mr Knight said: "The past 13 months has been hard for all the family, and I don't think we will ever come to terms with losing Ben. I have become aware since the accident through asking for information under the Freedom of Information Act that all was not well with the Nimrod fleet prior to the accident. The Nimrod XV230 [the aircraft in which his son died] had a large number of serious leaks in the months leading up to the crash, and some had not been rectified before flying as they were classed as acceptable leaks."

Nick Harvey, the Liberal Democrat defence spokesman, said: "In light of the mystery that still surrounds the Nimrod crash, one would be very concerned if there was the slightest hint of corners being cut or safety compromised." The Ministry of Defence said it was unable to comment.