Prince William, Prince Harry and Kate Middleton roar on 50,000 runners and celebrities in the London Marathon amid biggest security operation in 36 years

Prince William, Prince Harry and Kate Middleton together pushed the button to start the London marathon as hundreds of police lined the streets amid fears of a terror attack. The royals, who champion the marathon's official charity Heads Together, put their hands together to release almost 50,000 hopefuls on their gruelling 26-mile journey. Among them were celebrities including former Top Gear host Chris Evans, model Ashley James and Eastenders star Adam Woodyatt. Hundreds of police including armed patrols and officers with sniffer dogs are lining the streets of London for the biggest anti-terror operation in the 36-year history of the race. Security barriers have been set up near crowded spots including at the race start in Blackheath and at Tower Bridge to stop a Westminster-style vehicle attack. Police have been told they must 'shoot to kill' if they see a terrorist driver.