U.K. Prime Minister Theresa May has confirmed that the attacker in Wednesday's deadly terror attack outside the Palace of Westminster 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."

The identity of the attacker is known to both the Met and MI5, Britain's security services, but has not been identified to the public. In an official statement outside New Scotland Yard HQ in London earlier Thursday, Acting Deputy Police Commissioner Mark Rowley said that six addresses around the country had been searched, including during an overnight raid on a house in Birmingham, 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.

Four people -- including the alleged attacker -- died in the attack and forty more were injured, some of them gravely, after being struck by the speeding car, which reports say was rented by the attacker in the same area of Birmingham that was subject to the Met police search.

Westminster Bridge -- a busy connection point between north and south London across the River Thames -- remains closed Thursday as police continue the investigation amid what Scotland Yard has described as "large and complicated crime scene" while the city and the country remain on high alert.

Speaking to the House of Commons, the Prime Minister outlined what we know so far:

--At 2:40 pm GMT Wednesday, a single attacker drove a vehicle at speed Northbound across Westminster Bridge towards the Palace of Westminster.

--Two people were killed and 40 were injured on the bridge.

--Among the injured were 10 nationalities including 12 Britons, three French, two Romanians, four South Koreans and one American.

--Three police officers were also injured, two of the three are in a serious condition.

--The attacker then crashed the vehicle into the gates of Parliament, and stabbed a police officer. PC Keith Palmer died of his injuries.

--The attacker was then shot by an armed police officer.

--The Prime Minister chaired a Cobra meeting. The U.K.'s Threat Level remains at Severe, which has been for some time. This is the second highest level. May said the level was not raised to Critical as that mean there is evidence that a specific attack is likely.

--Police have carried out raids at six addresses across the country and eight arrests have been made in London and Birmingham.

--The Prime Minister said the attacker was British born and had previously been investigated for violent extremist behaviour by homeland security agency MI5.