Latest: Police name 52-year-old Westminster attacker

However, he was known to police and has a range of previous convictions for assaults, including GBH, possession of offensive weapons and public order offences.

The Prime Minister addressed MPs as they gathered at the usual time inside the Palace of Westminster, which a day before had come under attack from the knife-wielding terrorist.

An hour after MPs had stood for a minute’s silence in honour of the innocent people killed in the attack, Mrs May delivered a statement with details of the atrocity.

Paying tribute to Pc Keith Palmer, who died after being stabbed, she said: "He was every inch a hero and his actions will never be forgotten."

Describing the terrorist, Mrs May said: "What I can confirm is that the man was British-born and that some years ago he was once investigated by MI5 in relation to concerns about violent extremism. He was a peripheral figure.

"The case is historic. He was not part of the current intelligence picture. There was no prior intelligence of his intent or of the plot."

Mrs May concluded her statement by saying: "Our values will prevail."

Anti-terror police have arrested eight people in the wake of the attack.

Several addresses were raided overnight in London and Birmingham as Mark Rowley, the Met’s senior anti-terror officer, said he believed the attacker was working alone.

Director General of MI5 Andrew Parker also condemned the attack as "appalling and disgusting" and said the agency’s operational response is "fully mobilised in support of the police".

A minute’s silence was held nationwide at 9.33am, including in the Palace of Westminster and at New Scotland Yard, to commemorate the three innocent people who were killed.

The timing of the silence was chosen in honour of Pc Palmer’s shoulder number - 933.

MPs said they wanted to attend the House of Commons to show a commitment to freedom and democracy, and get "back to business".

Thursdays are often a quiet day in Parliament, with MPs travelling back to their constituencies or making trips elsewhere, but the chamber was packed for the minute’s silence.

Aysha Frade was the first member of the public to be identified as a victim, with her principal at DLD College London describing her as "highly regarded and loved".

She died along with Pc Palmer and a man in his mid-50s after the knife-wielding attacker ploughed a car through pedestrians on Westminster Bridge, before storming the Parliamentary estate. He was shot dead by police.

Forty people were hurt in the attack with 29 treated in hospital, where seven remained in a critical condition on Thursday.

The injured included 12 Britons, three French children, two Romanians, four South Koreans, two Greeks, and one each from Germany, Poland, Ireland, China, Italy and the United States. Three police officers were also hurt, two of them seriously.

At the scene of one of the police raids, a flat in Hagley Road, Birmingham, one witness told the Press Association: "The man from London lived here."

In London, swathes of Westminster remained cordoned off to the public on Thursday, with the site of the attack desolate except for crime scene tents, including one where the car crashed into the railings surrounding the Palace of Westminster.

• Four people were killed in the attack in Westminster yesterday. These were: Aysha Frade, 43; a man in his mid 50s, PC Keith Palmer and the attacker;

• 29 people were treated for their injuries in hospital; seven of these are critically ill; numbers of ‘walking wounded’ are still being collated;

• The attacker has not yet been publicly identified, and police have asked the media to not yet do so;

• Eight people have been arrested in raids at six addresses in connection with the investigation overnight; The raids took place in London, Birmingham and at other, undisclosed, locations;

• Metropolitan Police say the attacker acted alone, but was ‘inspired by international terrorism’;

• British Defence Secretary Michael Fallon has said the working assumption is that the Westminster attack is linked to Islamic terrorism;

• The Islamic State group has said through its Aaamaq news agency that the London attacker was a "soldier of the Islamic State".