London attack: Four people dead and 20 injured in Westminster terror incident

A body is covered by a sheet outside the Palace of Westminster, London, after a policeman was stabbed and his apparent attacker shot by officers in a major security incident at the Houses of Parliament (PA)

Four people were killed in the Westminster terror attack, police have confirmed.

The number includes the police officer who was stabbed and his attacker, Scotland Yard's top anti-terror officer Mark Rowley said.

The other two victims are understood to have died on the bridge, he added.

He also said at least 20 people had been injured.

Mr Rowley also said police believed there to have been only one suspect, although he said they were carrying out thorough checks.

The attacker, armed with two large knives, mowed down pedestrians with his car on Westminster Bridge, including schoolchildren, then rushed at the gates in front of the Houses of Parliament, stabbing a policeman before he was shot by armed officers.

Eyewitnesses described scenes of terror when gunfire rang out as the attacker approached a second officer within yards of the Houses of Parliament.

Mr Rowley told reporters outside New Scotland Yard: "This was a day we've planned for but hoped would never happen. Sadly it is now a reality."

Paramedics fought to save the officer's life and that of his attacker on the floor of the cobbled courtyard in front of Parliament, with Foreign Office minister Tobias Ellwood among those who rushed to help.

The police officer was wheeled away on a stretcher with his face covered.

Mr Ellwood, who lost his brother in the Bali bombing, could be seen pumping the officer's chest then standing above him, his hands and face smeared with blood.

Other armed officers, some in plain clothes and wearing balaclavas, swarmed around the yard just feet from where MPs had earlier attended Prime Minister's Questions.

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[22 March 2017 14:52 · Samuel Osborne]

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The Independent's deputy political editor Rob Merrick said: "Two men have been shot - one, presumably the assailant looked like he could be dead.

"The second, a police officer, was wounded but moving. I saw at least one man running towards the exit of New Palace Yard, underneath Big Ben.

"Police were shouting at him, presumably to stop and/or drop his weapon. I think I heard two shots.

"A police officer fell to the ground clutching his arm or shoulder.

[22 March 2017 15:00 · Samuel Osborne]

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Two people were seen lying within Old Palace Yard, immediately outside Westminster Hall.

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Minutes after the incident, an emergency services helicopter landed in Parliament Square, as sirens were heard outside.

Air ambulance medics came from the helicopter to assist the casualties.

[22 March 2017 15:02 · Samuel Osborne]

[22 March 2017 15:02 · Samuel Osborne]

Witness Don Brind told the Press Association he heard shots being fired and saw two people apparently injured on the ground.

Mr Brind, a researcher for MPs, said: "I heard some shouting and saw some running out of the corner of my eye and then a short time after that there was a shot. I looked and I saw a civilian on the ground, with somebody standing over him with what I assumed to be a gun.

"Then I looked and about 10 yards away, there was a yellow jacketed person on the ground, who appeared to be alive and talking."

He said he assumed the person in the high-visibility jacket was a police officer.

[22 March 2017 15:06 · Samuel Osborne]

To clarify earlier reports: A police officer been stabbed and an alleged assailant shot by armed police.