Leeds Town Hall flags to fly at half mast in honour of London terror attack victims

The council announced the decision late on Wednesday night that the flags will be lowered to half mast on Thursday morning.

The attack, which left three people dead as well as the attacker, shut down London as thousands of people were trapped inside Parliament.

The Prime Minister has vowed to defeat what she called "the forces of evil" after four people, including a police officer, were killed when a knifeman brought terror to the heart of Westminster.

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 the policeman before being shot dead by other officers.

Mrs May, who was in Parliament at the time of the attack, praised the bravery of police officers who killed the attacker as he sought another victim.

And she said that any attempt to defeat the values that Parliament stands for was "doomed to failure".

The four dead included the police officer, the knifeman and two people who were killed on the bridge as the terrorist sped toward Parliament.

At least 20 other people were hurt, with some said to have suffered "catastrophic" injuries.

Eyewitnesses described scenes of terror when gunfire rang out as the knifeman lunged towards a second officer.

Scotland Yard's top anti-terror officer Mark Rowley told reporters outside New Scotland Yard, just yards from the scene of the attack: "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.

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.

Donald Trump was among world leaders quick to offer their support.

The White House said the US president spoke to Mrs May in a phone call following the bloody events in London.

The knifeman drove a grey Hyundai i40 across Westminster Bridge before crashing it into railings then running through the gates of the Palace of Westminster.

His attack left a trail of destruction as paramedics tended to victims on the bridge and at the gate.

One woman hit by the attacker's car before he reached Parliament was confirmed dead by a doctor at St Thomas' Hospital. She said others on the bridge suffered "catastrophic injuries".

Another woman who fell into the Thames was rescued and given urgent medical treatment on a nearby pier.

London Ambulance Service said paramedics had treated at least 10 patients on Westminster Bridge.

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

Mobile phone footage showed a woman lying lifeless under a bus on the bridge near where the car crashed to a halt.

Eyewitness Rick Longley said: "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."

Rob Lyon, 34, from Rugby, Warwickshire, was walking along Westminster Bridge with a colleague when he saw the car travelling at high-speed, hitting pedestrians.

He said: "I heard a wheel definitely hit a kerb, quite a loud crunch noise, I looked up and saw a car clearly hitting people as it came towards me.

"A colleague I was with, James, I heard him sort of shout. I instinctively jumped off the pavement. I could see people being hit.

"And then the car just carried on up the bridge and I just looked around and was really in shock."

He said he saw about five people lying on the ground around him.

"(I saw) people that had been hit by a car at speed - it was harrowing," he said.

Steve Voake, 55, was walking across the Westminster Bridge towards the South Bank when he saw the aftermath.

He said he saw at least two bodies lying on the road and one in the water.

"I saw a trainer lying in the road and when I looked more closely I saw that there were a couple of bodies the other side of the road," he told the Press Association.

"And when I looked over the side there was another body lying in the water with blood all around it."

An air ambulance landed in Parliament Square and a regular ambulance came in through the front gates as medics rushed to help the police officer.

Armed police cleared the area around the incident and Parliament Square and surrounding streets were closed to traffic while Parliament went into lockdown.

Witnesses described seeing a heavy-set man carrying a knife and running towards the Houses of Parliament.

Jayne Wilkinson said: "We were taking photos of Big Ben and we saw all the people running towards us, and then there was an Asian guy in about his 40s carrying a knife about seven or eight inches long.

"And then there were three shots fired, and then we crossed the road and looked over. The man was on the floor with blood.

"He had a lightweight jacket on, dark trousers and a shirt.

"He was running through those gates, towards Parliament, and the police were chasing him."

Frazer Clarke, 25, from Burton-on-Trent, Staffs, one of a group of young boxers who witnessed the attack, said: "We heard a loud bang and screaming and then I noticed some smoke. I thought it was a car crash.

"I looked towards the front gate and people were running, a police officer and a fellow coming to the gate with two knives.

"He was stabbing the police officer with the knives.

"He was wearing black tracksuit bottoms, a black or grey top and what looked like work boots.

"The police officer was stumbling and fell on the floor.

"Another police officer walked toward the guy with the knives and shot him twice."