Stop the scams involving helicopter evacuations or we will exclude Nepal from coverage: that is the message from the travel insurance industry to the government of the Himalayan nation.

A trio of insurance underwriters have given the tourism minister in Kathmandu, Rabindra Prasad Adhikari, an ultimatum. Between them they cover over 100,000 visitors annually to Nepal.

They are demanding an end to what they call an “elaborate scam” that has “defrauded millions of dollars from global travel insurance companies” and even claimed lives, according to experts.

The accusation centres on helicopter evacuations from high-altitude locations such as Everest base camp, the high point for many treks. Each flight costs thousands of dollars, and some bills are inflated by fraudulent commission payments to trekking firms and guides.

One experienced UK guide in Nepal, who wanted to remain anonymous, called it “the instant Everest base camp scam”, saying: “You go up, throw up and come down. Usually by rescue helicopter, with 30 per cent commission to your guide or agent.”

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In some cases, foreign visitors connive with the trekking firms. They are offered cut-price expeditions from Kathmandu on the understanding that they will feign acute mountain sickness (AMS, colloquially known as altitude sickness) and ask for a helicopter rescue. Their insurance documents are checked before they are accepted on the trip to ensure that the helicopter firm and its “agent” will be paid off.

It is alleged that other trekkers are made temporarily unwell by “spiking” their meals with baking soda, uncooked chicken or even rat droppings.

The scam is said to have cost lives. Leading figures in Nepal’s tourism industry have told The Independent of cases in which the evacuation of genuinely ill trekkers has been delayed until a helicopter known to pay commission was available. Before the “approved” rescue can happen, the victim has died.

World Nomads, based in Sydney, now warns trekkers to Nepal that they must get approval from its emergency assistance team before a helicopter rescue, saying: “Helicopter operators inflate flight hours to gain more money and guides of trekking companies gain commission payments as a result of calling for the helicopter evacuation of insured trekkers.

“All of this results in the insurer paying unnecessary bills, and trekkers often being taken off the mountain when they didn’t need to miss out on the rest of their trek.”

Some guides, it is alleged, have two mobile phones. They call the assistance company on one to warn them a trekker is ill, then turn it off so they cannot be instructed to halt the evacuation. Meanwhile they coordinate the “rescue” on their other phone.

Since the symptoms of AMS disappear once the patient is at low altitude, it is impossible to say with hindsight whether the evacuation was necessary.

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Sometimes a number of trekkers are carried on a single flight but are charged for individual rescues. The insurers say that helicopter firms are being paid commission by hospitals for delivering patients to them.

The letter says that unscrupulous companies are “pushing trekkers to agree to a helicopter for minor illnesses, multiple claims for a single helicopter and overtreatment at hospitals.

“All of these added costs would be billed to the insurer through inflated helicopter and medical bills.”

The letter was hand-delivered to the Ministry for Culture, Tourism and Civil Aviation by Danny Kaine of the assistance company Traveller Assist.

He told The Independent: “In 2018, after an extensive investigation, our company uncovered an elaborate scam that defrauded millions of dollars from global travel insurance companies.”

Details of the investigation were passed on to the ministry, he said, which promised to clamp down on the practice – as well as prosecuting offenders for fraud and tax evasion.

But, he says: “Not a single charge has been laid.”

The letter tells the tourism minister: “If our clients stop issuing travel insurance policies in Nepal, it won’t be long until other insurers do the same. This will have a devastating effect on the tourism industry in Nepal, and your country’s reputation.”

The move would not affect policies issued before 15 February 2019.

Mr Kaine said: “My worry is that people will still go there but they won’t be insured.”

As a proactive measure, Traveller Assist is setting up a booth at Kathmandu airport to advise arriving trekkers about how to avoid AMS and remain healthy.

The firm is also deploying medics to two key locations from which there are frequent evacuations, in order to assess patients before a helicopter is summoned.

It has offered to help the government in Nepal to investigate the alleged practices.

Nepal’s embassy in London has rejected the accusations, saying: “This is not true. Government is always looking [at] this matter seriously and taking necessary measures to ensure the safety of the tourists and also facilitates travel insurer for their concern.”