The Who Wants To Be A Millionaire host, 67, fell ill during the 11-hour flight and was rushed to hospital from Heathrow Airport.
At first doctors thought that he had suffered an asthma attack, but they went on to find a potentially fatal blood clot in his leg and performed an emergency operation before it could dislodge and cause a major stroke.
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The former radio host has also developed bronchitis.
On Tuesday evening Chris’s agent and manager Paul Vaughan confirmed that: "They found a clot which they managed to break up."
He added: "It was a clot in the leg and that can immediately go to the brain or lungs." According to the agent, this has been a "nasty wake-up call" for the TV personality, who is "determined to leave hospital" but is "not going back to work."
Chris Tarrant hosting hit show Who Wants To Be A Millionaire
Chris was returning to the UK after filming a new travel series in Burma, which is due to air on Channel 5 later this year, when he began to feel ill and told the plane's crew that he would need an ambulance upon his arrival in the capital.
The 67-year-old father-of-four was met by emergency services on the runway and immediately taken to Charing Cross Hospital in central London.
While he is still at the hospital, he has been permitted daytime trips to his London flat in recent days.