Britain's entire fleet of Harrier jump jets, the veteran plane scrapped in last year's defence review, has been saved - by the American military.

All 74 of the planes are to fly again for the US m arines in a deal that is expected to be closed within a week.

The Ministry of Defence said last night that negotiations were in their final stages. Reports in the US suggested the Marines were already preparing for their arrival.

The sale of the Harriers is bound to raise fresh questions about the wisdom of retiring the much-admired aircraft, which the Americans intend to use until 2025.

Speaking to the NavyTimes, Rear Admiral Mark Heinrich, chief of the US Navy's supply corps, said buying the Harriers made sense because many of the jets had been recently upgraded, and the US already had pilots who could fly them.

"We're taking advantage of all the money the Brits have spent on them," he said. "It's like we're buying a car with maybe 15,000 miles on it. These are very good platforms."

News of the sale comes as the government spending watchdog has found that the UK's biggest military projects are more than £6bn over budget, and are suffering from further delays despite attempts to bring them under stricter control.

The National Audit Office report also states that the UK faces a potential shortage of attack submarines because of cost-cutting decisions taken in last year's strategic defence and security review.

In a 70-page study, the NAO says the total cost of 15 equipment programmes has reached £59.6bn, and that - on average - they will be 30 months late into service. The watchdog says the MoD is still reeling from mistakes made more than a decade ago, but concedes that the department is slowly bringing things under control.

The NAO sets out continuing attempts by the MoD to bring down spiralling costs on projects that include the construction of seven Royal Navy Astute class submarines, the RAF's Typhoon fast jets, and updates designed to breathe new life into older equipment.

The MoD had forecast the total overall costs for these projects would be £53.5bn, but that has now been revised to £59.6bn.

The chaotic Astute submarine programme is singled out in the NAO report. Initially, eight of the attack submarines were due to be built, but that was cut to seven because of costs, and the programme has now been delayed so that the last of the boats will not be in service until 2024 - almost three years late.

Amyas Morse, head of the National Audit Office, said the MoD had been "hampered by a legacy of poor planning and performance on some past projects, and the resulting cuts and delays are not value for money". The defence secretary, Philip Hammond, said the MoD had made progress and was now "balancing its books". The MoD also disputes that the delay to the Astute programme will lead to a capability gap.

