Chris Tarrant was reportedly rushed to hospital after collapsing in the baggage area at Heathrow Airport on Saturday.
The Who Wants To Be A Millionaire star apparently started feeling unwell on his Thai Airways flight home from Bangkok.
He then collapsed while picking up his luggage at Terminal 3.
A source told the Daily Star Sunday: "Paramedics were quickly on the scene and were desperately treating him.
"Other passengers were in a state of shock and were moved away by security staff."
Paramedics were on the scene within minutes and the 67-year-old was rushed to London's Charing Cross Hospital.
The star's agent Paul Vaughn said he had been filming a second series of Chris Tarrant: Extreme Railways, and had been in the Andes and Burma before heading back to the UK via Bankgkok.
According to Mr Vaughn, the health scare was an asthma attack.
He told the Daily Mail: "I've been his manager for 30 years, and I know that if he goes down like a ton of bricks it's usually asthma.
"I'm surmising, but I think his asthma attack might have been triggered by a night-time stopover in Bangkok, which has very poor air quality."
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