A policeman and two members of the public are among four people killed in a major terrorist incident at the Houses of Parliament.

Pc Keith Palmer, who was stabbed while trying to protect Parliament, died along with a woman in her mid 40s and a man in his mid 50s. The killer, who is as of yet unnamed, also died.

This morning, the Met’s top anti-terror officer Mark Rowley said 29 people had been treated in hospital and seven remain in a critical condition following the attack in which several pedestrians were mowed down on Westminster Bridge.

He added: “As people are out and about on the streets of the capital this morning they will see more police officers on duty - armed and unarmed - and a mix of British Transport Police and the City of London.

“We have cancelled some leave and increased some duty hours and are working to make sure that we can out in force to reassure the public.

Seven people were also arrested overnight following raids in London, Birmingham and elsewhere, police confirmed.

Defence Secretary Sir Michael Fallon said the “working assumption” was that the attack was linked to “Islamic terrorism in some form”.

Prime Minsister Theresa May praised the bravery of police officers, saying: “Any attempt to defeat those values through violence and terror is doomed to failure.”

She said the House of Commons and the House of Lords will sit at their normal times today.

It has also been confirmed that a party of French schoolchildren were among those targeted on the bridge.

Four students from Edge Hill University in Ormskirk were also hurt - two described as “walking wounded”, and another couple were said to have minor injuries.

Eyewitness Rick Longley described the attack.

“We were just walking up to the station and there was a loud bang and a guy, someone, crashed a car and took some pedestrians out.

“They were just laying there and then the whole crowd just surged around the corner by the gates just opposite Big Ben.

“A guy came past my right shoulder with a big knife and just started plunging it into the policeman.

“I have never seen anything like that. I just can’t believe what I just saw.”

Police are asking people to avoid the following areas: Parliament Square; Whitehall; Westminster Bridge; Lambeth Bridge; Victoria Street up to the junction with Broadway and the Victoria Embankment up to Embankment tube.

What we know so far:

:: A massive police operation is under way after an attack in the heart of central London.

:: Four people have died - a police officer, the attacker, a woman in her mid 40s 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

:: Seven 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

:: 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”