A man is fighting for his life in hospital after having a cardiac arrest on Westminster Bridge in London. Police were called to the bridge near the Houses of Parliament to an alleged fight at about 10.45am on Sunday. Initial reports from central London said that the man had been stabbed but the Metropolitan police later said this was incorrect. Detectives are investigating how the man came to suffer a cardiac arrest. He was still in hospital, in a critical condition, on Sunday evening. London air ambulance and the London ambulance service attended the scene along with police. Three people were arrested on suspicion of attempted murder, and one person on suspicion of affray. Two of those arrested were taken to hospital with head injuries. Police have urged anyone who witnessed the event to come forward, and asked anyone who has CCTV, mobile phone or dashcam footage to contact officers. Anyone with information or footage can contact police on 101, quoting crime reference number 2468 of 24 November. Alternatively, they can contact the independent charity Crimestoppers anonymously on 0800 555 111.