Three military jets – part of a fleet costing taxpayers an astonishing £10.5 billion – are being used to fly holidaymakers to sun-kissed resorts because the RAF has no use for them.

The aircraft are supposed to transport British troops to military bases around the world and refuel fighters and bombers in mid-air during combat sorties.

But a Mail on Sunday investigation can reveal that while the cash-strapped Ministry of Defence shells out tens of millions of pounds a year for the planes, holiday firms Thomas Cook and Jet2 have been using them to fly thousands of tourists to Majorca, Tenerife, New York and Florida.

Military service: The jets were meant to be used by the RAF to transport British troops

Prince Harry, right, took this Voyager back to the UK after a tour of Afghanistan in 2013

The aircraft are among 14 Airbus A330s acquired by the MoD under a controversial leasing agreement which costs about £400 million a year.

The deal with a consortium of aviation manufacturers called AirTanker allows the commercial group to potentially make millions more by renting up to four of the unused aircraft to holiday firms.

Last week, The Mail on Sunday boarded one of the planes in Manchester and flew with hundreds of tourists on Jet2 package breaks to Tenerife. We also tracked two other RAF planes over the past week as they flew Thomas Cook holidaymakers from Manchester to New York, Seattle, Boston and Orlando.

MoD documents seen by The Mail on Sunday reveal that all three aircraft, which in their military role are called Voyager, remain part of the RAF’s fleet. It is understood they have never been used on operations, although the MoD refused to confirm this last night.

The military jets are supposed to be used to refuel fighters and bombers in mid-air during combat sorties (pictured)

We can also reveal that:

- The MoD is forced to pay more for any of the planes if they fly into war zones because AirTanker does not insure them;

- AirTanker charged £94 million for an aircraft hangar which experts say should have cost much less;

- The Australian Air Force bought the same model of aircraft for tens of millions of pounds less.

Heading for the sun: Our view inside the Jet2 A330 which was destined for Tenerife last week

Documents, pictured, show it was operated by AirTanker - the aviation manufacturer which leased MoD the jets

The astonishing revelations come just weeks after Defence Secretary Gavin Williamson threatened to sweep Theresa May from power in a bitter Cabinet row over military cuts, demanding an extra £20 billion over the next decade.

The Mail on Sunday understands Mr Williamson is frustrated about the cost of Voyager, while Lord Dannatt, the former head of the British Army, described the deal as a ‘national scandal’.

A source close to Mr Williamson said: ‘Poor historic deals like this are squeezing the defence budget and leaving no room to manoeuvre. Voyager is one of the reasons we have to fight for more funds to avoid devastating cuts elsewhere.’

The controversial agreement between the MoD and AirTanker was signed off in March 2008 when Gordon Brown was Prime Minister, Alistair Darling was Chancellor and Des Browne was Defence Secretary. They agreed to lease 14 Voyagers from AirTanker, a consortium which included French-based manufacturer Airbus and engine-maker Rolls-Royce, under a Private Finance Initiative (PFI) arrangement.

According to one contract seen by the MoS, Airbus was selling A330s for around £50 million in 2007, so a fleet of 14 would have cost £700 million to buy outright. Our investigation suggests the deal the MoD signed was based on a figure closer to £200 million for each plane, with the rest of the £10.5 billion covering financing, operating the service and infrastructure. The total could even rise to £12.3 billion once staffing and fuel costs are included.

The costs are paid back over 27 years, with repayments expected to peak at £593 million in 2034.

The deal also allows AirTanker to lease aircraft to commercial airlines when the RAF is not using them. But the MoD continues to pay huge sums for the right to take back the planes and use them on military operations if required. Last night, defence officials refused to confirm the cost, claiming the figure was ‘commercially sensitive’.

Jet2 have been using them to fly thousands of tourists to Majorca, Tenerife, New York and Florida

It takes less than a month to refit the jets to switch between military and civilian use.

The Voyager deal was heavily criticised soon after it was signed. A report by the National Audit Office said it was too expensive, uncompetitive and overly complicated, and that the MoD lacked the expertise to manage the project.

Our disclosures highlight the problems with PFIs, under which the private sector takes on major public projects such as schools and hospitals, but saddles the taxpayer with debts – which some experts say total £300 billion.

The Mail on Sunday also understands that it would cost the MoD £3.5 billion to buy its way out of the Voyager contract.

Military experts say the money spent on this deal would have been better used on equipment which could have saved soldiers’ lives in Iraq and Afghanistan, such as armoured vehicles to protect squaddies from roadside bombs.

Getaway: One of the aircraft, in Thomas Cook livery, heads from Manchester to Orlando last week

Last night, former Armed Forces Minister John Spellar said: ‘The bottom line is that bad deals like this cost lives. Voyager has left the MoD so short of cash that troops have gone without top-grade equipment. They’ve also been paid less and been forced to live in inadequate accommodation. Billions of pounds have been wasted and a private consortium has been able to cream off huge profits.’

It is unclear how much military service the Voyager fleet has seen. But some aircraft are being used as troop carriers to and from bases in the UK, Cyprus and the Falkland Islands. In April this year, a Voyager refuelled Tornados in the international mission to destroy alleged chemical weapons facilities in Syria.

One of the Voyagers was also given a £10 million refit so it could be used by the Prime Minister, senior Ministers and members of the Royal Family, including Prince Charles, for use on official long-distance trips. Prince William used it for a recent trip to the Middle East.

As part of the deal, AirTanker built a hangar at RAF Brize Norton in Oxfordshire for maintenance work. Its accounts say this hangar cost £94 million, but aviation industry sources believe it could have been built for significantly less. It would also appear cheaper for the MoD to purchase Voyagers directly from the manufacturers. In 2015, the Royal Australian Air Force bought Airbus refuelling and passenger jets for just over £100 million each.

The Mail on Sunday supplied AirTanker with a detailed list of questions about the Voyager deal, but it declined to comment.

The MoD said: ‘Voyagers are playing a key role in protecting British airspace and in the fight against Islamic State, and while our core fleet is doing the job we need it to, we can call in the extra aircraft at short notice if we need them.

‘When we’re not using them it makes sense to have them performing other roles, as that reduces our costs and means they can be ready for operations quicker than if they were held in storage.

‘This is a cost-effective deal that is delivering an outstanding service for the RAF.’

As bad as PFI deals go, this was the worst of the lot

Comment by LORD DANNATT, former Army head

Buying something you couldn’t really afford was taken to a new level in the 1990s under the Private Finance Initiative.

The government of Tony Blair and Gordon Brown seized on the concept to produce shiny new schools and hospitals across the country, especially in marginal constituencies.

But the Voyager PFI deal has to rank as the worst of the lot. Even at face value, £10.5 billion to lease 14 aircraft does not seem like value for money.

The project was led not by an RAF officer, but by an Army brigadier, so that there was no undue service bias.

But this brigadier was so alarmed at the way it was going that he came to me in 2008, while I was Chief of the General Staff, to ask if I could try to get this deal stopped.

I asked for a briefing, having been told there were much cheaper ways to meet the RAF’s air-to-air refuelling and strategic lift requirement.

At the briefing, all other options were dismissed for one spurious reason or another, leading to the curious conclusion that the £10.5 billion procurement of 14 A330 airliners, assembled at Airbus Industrie’s factory near Madrid, was the answer.

In the end, the politics of European industrial collaboration was the winner, the MoD was the loser, and now bucket-and-spade holiday-makers are travelling to sunny places overseas at British taxpayers’ expense. Is that value for money?

Defence Secretary Gavin Williamson’s Modernising Defence Programme must put a stop to scandals like this.