Sir Jackie Stewart is in a London hospital after falling ill during a flight from the Geneva motor show.
The 71-year-old former triple world champion is reported to have suffered chest paints and passed out.
"I've just spoken to him in hospital. He seemed absolutely fine but obviously something happened and we need to establish what, but I'm on my way to see him right now," his son Paul told the BBC.
The Scottish newspaper Daily Record said the plane was met by paramedics at Heathrow airport on Wednesday. The Mirror said he was taken to Hillingdon in west London.
British Airways confirmed: "Our flight crew requested a priority landing so that a male passenger could receive medical attention immediately on arrival."