London Metropolitan Police have named the man they say carried out yesterday's deadly terrorist attack outside the Palace of Westminster that left four people dead and dozens more seriously injured.

In a statement from New Scotland Yard HQ in London, the Met said that Masood was born in Kent but had been living in an area of England known as the West Midlands. The Met said Masood had been known to police and had a "range of previous convictions for assaults, including [grievous bodily harm], possession of offensive weapons and public order offences" and was first convicted for knife possession in 1983.

Earlier Thursday, U.K. Prime Minister Theresa May confirmed that the attacker was British-born and had previously been investigated for extremist behaviour by the country's security services.

Speaking to lawmakers during a special session of Parliament in the House of Commons -- only a few metres from where yesterday's deadly terrorist attack took place -- May described the alleged assailant as a "a peripheral figure" but repeated the Metropolitan Police's view that the "working assumption is that the attacker was inspired by Islamist ideology." May reiterated her stance that the business of government can and must continue.

"Yesterday an act of terrorism tried to silence our democracy. But today we meet as normal, as generations have done before us and as future generations will continue to do, to deliver a simple message: we are not afraid and our resolve will never waver in the face of terrorism," May told lawmakers. "And we meet here in the oldest of all parliaments because we know democracy and the values it entails will always prevail. Those values free speech, liberty, human rights and rule of law are embodied here in this place and shared by free people around the world."

Acting Deputy Police Commissioner Mark Rowley also said that six addresses around the country had been searched, including during an overnight raid on a house in Birmingham, in the West Midlands, and that eight arrests had been made.

Police have also confirmed that name of the officer murdered in yesterday's attack as 48-year old PC Keith Palmer, who died after receiving multiple stab wounds from the attacker, who appears to have driven his car at speed along Westminster Bridge, which runs adjacent to Parliament, striking several pedestrians -- two of whom later died -- before lunging at PC Palmer with two large knives.

ISIS has claimed responsibility for Wednesday's attack, according to multiple media reports that cite an Arabic-language statement from group called Amaq, an agency used to broadcast the terrorist organisation's propaganda.

"The attacker yesterday in front of the British parliament in London was a solider of the Islamic State, executing the operation in response to calls to target citizens of coalition nations," the statement said, according to an English translation.