It is claimed that RAF Northolt in west London — home to the Queen’s Flight — has given NetJets Europe, a corporate jet company partly owned by Warren Buffett, the American billionaire, special access to the base.

Other private jet owners who have been refused permission to land are said to be “seething” over the allocation of the coveted landing slots. NetJets has 3,500 landing slots, half of the annual total available for civilian flights.

“This is a base funded by the British taxpayer, but a clear commercial advantage is being given to a foreign operator,” said one senior figure in the private jet sector, who asked not to be identified. “At weekends, you can see American-registered Gulfstreams flying in and out while British planes are not allowed to land. You have to ask what the hell is going on.”

The jets — used by celebrities such as Liz Hurley, Tim Henman and Hollywood actor Matt Damon — are routinely allowed to land at Northolt in the evenings and weekends when the airport is officially closed to most other civil air traffic. The airport is popular among VIPs because it is near central London.

An MoD police spokesman said this weekend: “We are liaising with MoD officials over allegations relating to civilian contracts at RAF Northolt.”

He said inquiries were “at an early stage”, but it is understood a formal investigation may be launched next month.

NetJets, based in Portugal, said it was entitled to so many landing and takeoff slots at the military airport because some of its jets were based there. It says it has done nothing wrong.

NetJets Europe is the biggest operator of business jets in Europe and has about 100 aircraft in its fleet. Its American arm is owned by Buffett, who is the second richest man in the world with a personal fortune estimated at £24 billion.

Buffett also has shares in the European operation. Under a scheme of “fractional ownership”, NetJets gives companies and individuals the chance to buy a stake in a corporate jet.

Executives at many large companies use the jets rather than travel by scheduled airline. Celebrities have also opted for the service, which costs about £3,000 for each hour of air travel. rather than face the costs of paying for their own plane. Madonna, Bono and Arnold Schwarzenegger are among the stars said to use the jets.

Northolt is home to No 32 (the Royal) Squadron, formerly known at the Queen’s Flight. It is the main airport used by Tony Blair and ministers for international and domestic flights.

Although other private jets are allowed to use Northolt, they are not granted the access that NetJets has in the late evening or at weekends.

It is understood NetJets secured access to Northolt by going into partnership with Northolt Business Aviation, which operates a hangar at the base. Northolt Business Aviation was awarded a contract to operate at the base in about 2002 and the deal allowed NetJets to operate from there.

Other private jet operators are now questioning the tender process involved and the current terms of the contract that allows NetJets such a big proportion of landing and takeoff slots. The operators of two private jets based at RAF Northolt have been requested to leave amid allegations that NetJets will now be allowed to use some of their landing slots.

Other jet company executives are understood to be consulting lawyers on the legality of the current allocation of landing slots to NetJets. The MoD declined to comment on details of the contract.

A spokesman for NetJets Europe said: “[The company] is treated no differently from any other. As a fixed-based operator, NetJets Europe is allocated a set number of slots. For its remaining slots NetJets applies and has the same access as any other operator.”

Peter Riley, a director of Northolt Business Aviation, denied any improper behaviour in the awarding of contracts at the RAF base. “They are almost impossible to deal with because they have to be seen as whiter than white,” he said.

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