Within eight minutes police were on the scene and eight officers opened fire, releasing 50 rounds and killing the three attackers.

Photos on social media showed two of the men on the ground. One of them, in front of the Wheatsheaf pub, had what appeared to be canisters strapped to his abdomen. Police later said that the canisters were fake.

What do we know about the attackers?

Khuram Butt was a 27-year-old British citizen born in Pakistan but lived in Barking, east London where he was believed to live with his wife and two children. The couple were said to have had an arranged marriage.

He had been reported to the anti-terror police on at least two occasions, it was claimed.

Assistant Commissioner Mark Rowley said Butt was known to the security services, but there was no evidence of "attack planning" by him.

A former friend of the terrorist claimed he had been radicalised watching videos on YouTube and said he contacted the authorities after becoming concerned over his obvious extremist views.

Butt was seen praying with a group of radical Muslims in Regent’s Park in the Channel 4 documentary, including Mohammed Shamsuddin who was filmed warning that the black flag of Islam would one day fly over Downing Street and calling for Britain to adopt Sharia law.