A man who killed four people - including hero police officer Keith Palmer - in a terror attack in central London was born in Britain and previously investigated for "violent extremism".

In a defiant address to the House of Commons Theresa May said the suspect - named as Khalid Masood, 52 - "was investigated by MI5 over concerns about violent extremism” in the past.

She said there was “no prior intelligence of his intent, or of the plot, but intensive investigations continue," she added.

The terror group ISIS later claimed the attacker as one of their own, saying he was a "soldier of the caliphate".

(Image: REUTERS)

Tonight thousands of people turned out to a vigil in Trafalgar Square to mourn the people who lost their lives and show solidarity in the face of terrorism.

It was also confirmed that a 75-year-old man who had been in hospital following the attack has now passed away.

Read a recap of our coverage of the attack and its aftermath below.