A massive police investigation is under way after a terror attack in central London.

Here’s everything we know so far about the Westminster attack:

Four people have died – a police officer, the attacker, a woman named as Aysha Frade, 43, and a man in his mid 50s.

The officer was Pc Keith Palmer, a 48-year-old husband and father with 15 years of police service.

A minute’s silence was held at 9.33am to honour Palmer, whose police shoulder number was 933.

Eight people have been arrested and six addresses raided across London, Birmingham and elsewhere.

The woman was killed on Westminster Bridge as a number of pedestrians were mowed down by a grey Hyundai i40.

It is believed the man was also killed in the incident on the bridge.

Seven people are in a critical condition, and 29 have been treated in hospital.

One woman ended up in the Thames and was treated for serious injuries after being pulled from the water.

The attacker, armed with two large knives, jumped out of the car after smashing it into the railings encircling the Palace of Westminster, fatally stabbing Pc Palmer as he entered the grounds.

He was shot dead moments later by another officer.

During a speech in Parliament, Theresa May confirmed the Westminster attacker was a British citizen who was known to the police and security services, and had been investigated some years ago over violent extremism.

May told MPs he was a ‘peripheral’ figure, adding: ‘He was not part of the current intelligence picture.’

Here’s everything we know about the attacker.

Defence Secretary Michael Fallon has said the working assumption is that the attack is linked to Islamic terrorism.

A group of French schoolchildren were among those targeted on the bridge, with three injured.

Prime Minister Theresa May later chaired a meeting of the Government’s emergency Cobra committee, branding the attack ‘sick and depraved’.

To see all of our coverage of the London terror attack click here.