You might have seen reports that former Top Gear host Richard Hammond and his family were "gassed and robbed" at a holiday villa in St Tropez, France, last month.

They're not the first celebrities to claim they have had gas used against them in a robbery attempt, but medical experts are sceptical about claims of burglars using gas.

This is what the family says happened and why an increasing number of celebrities think burglars are using gas on unsuspecting tourists.

What happened

Richard's wife Mindy Etheridge said the couple's teenage daughter Willow and a group of friends woke up one morning to discover cash had been stolen from their wallets and purses, and a watch swiped from Willow's room.

Writing in the UK's Sunday Express, Mindy says she is "pretty convinced" the family were gassed in their sleep because the robbers allegedly spent time rummaging through every room and drawer in the house.

It wasn't until the next morning, when Willow couldn't find her watch, that the family realised they had been robbed.

Mindy said she suspected they were "gassed" because the family, and the 15 other guests staying in the villa, slept through the ordeal and late into the following morning.

The burglars were caught on CCTV and arrested several days after the incident.

Why they're 'pretty convinced'

Thieves are reported to have previously pumped anaesthetic gas through air conditioning systems in a series of raids on luxury villas in France.

In 2015, British ex-Formula One driver Jenson Button and his wife Jessica were robbed while staying on the French Riviera.

According to Button's spokesman, French police said air-vent gassing was familiar to them in the wealthy holiday region.

Cities along the French Riviera are known for their affluence. ( Reuters: Charles Platiau )

Prior to that, former Arsenal footballer Patrick Vieira, said an anaesthetic gas was pumped through the air-conditioning system while his family slept in a holiday villa in Cannes.

And in 2002, British television stars Trinny Woodall and Susannah Constantine said they were gassed while attending the Cannes Film Festival.

There have also been many stories of tourists in campervans being gassed and robbed at service stations in France and neighbouring countries.

In response, the British Foreign Office and US Embassy in France issued statements warning travellers to be alert and ensure their windows and doors were locked at night.

Why medical experts aren't convinced

But in 2014, in response to the campervan incidents, the British Royal College of Anaesthetists (RCOA) said it was the college's view that gassing was "a myth".

"It is the view of the College that it would not be possible to render someone unconscious by blowing ether, chloroform or any of the currently used volatile anaesthetic agents, through the window … without their knowledge, even if they were sleeping at the time," the College said in a statement.

"[Also] these drugs would be too expensive for the average thief to use."

General anaesthetics are either inhaled or administered from pressure tanks and they have odours and health risks associated with them.

The college says there is no anaesthetic in existence that is "safe, odourless, potent [and] cheap enough" for the average person obtain or handle.

If there was one, the College says, it would "know about it and be investigating its use in anaesthetic practice".