A 28-year-old doctor from London, reportedly on two years' leave from his post, has been leading a terror group in Syria, according to The Sun.
The doctor, who had reportedly worked as a junior doctor under the National Health Service (NHS), may have treated thousands of patients in 16 different hospitals.
Police and health chiefs have launched investigations after it was reported that the doctor-led group kidnapped British photographer John Cantlie in Syria.
The General Medical Council said the man may have worked rotational shifts in various departments across London's different NHS hospitals as part of his training.
The kidnapped photographer told The Sun how he was abducted and shot at by Islamic fanatics led by a "gun-toting doctor" from London.
The doctor told him he worked for a leading London hospital but had gone to Syria to fight the "holy war". He planned to return to Britain to take a top job in a hospital.