Parliament will put on a show of stoic defiance when MPs attempt to go about their daily duties, less than 24 hours after a terror attack brought death and destruction to the heart of London.

Both the House of Commons and the House of Lords will sit at their normal times on Thursday, despite Westminster playing unwilling host to the massacre the previous day.

PC Keith Palmer, a member of the Parliamentary and Diplomatic Protection Squad, was killed as he tried to stop the attacker at around 2.30pm on Wednesday, while three members of the public were also fatally injured.

The suspect, who was armed with two knives, injured around 40 others as he mowed down pedestrians with a car on Westminster Bridge before crashing at the gates in front of Parliament and stabbing the policeman before being shot dead by armed officers.

Theresa May praised the bravery of police officers on Wednesday night as it was announced Westminster would attempt to run as smoothly as normal.

In a statement from Downing Street, the Prime Minister said: “Any attempt to defeat those values through violence and terror is doomed to failure.

“(Thursday) morning, Parliament will meet as normal. We will come together as normal.

“And Londoners - and others from around the world who have come here to visit this great city - will get up and go about their day as normal.

“They will board their trains, they will leave their hotels, they will walk these streets, they will live their lives.

“And we will all move forward together, never giving in to terror and never allowing the voices of hate and evil to drive us apart.”

Shortly after 1.30am (GMT), the US President tweeted: “Spoke to UK Prime Minister Theresa May today to offer condolences on the terrorist attack in London. She is strong and doing very well.”

Meanwhile counter-terror detectives will continue searching for clues about how an armed attacker wrought destruction on London.

Speaking outside Scotland Yard on Wednesday night, acting deputy commissioner Mark Rowley, the Met's senior anti-terror officer, said police believed the suspect was “inspired by international terrorism” - and they believed they knew who he was.

Paying tribute to PC Palmer, who had served the police for 15 years, Mr Rowley said: “Today in Westminster we saw tragic events unfold and our thoughts are with those who lost loved ones, those who were injured and all those affected by this attack.

“One of those who died today was a police officer, PC Keith Palmer, a member of our parliamentary and diplomatic protection command. Keith, aged 48, had 15 years' service and was a husband and father.

“He was someone who left for work today expecting to return home at the end of his shift, and he had every right to expect that would happen.”

The attack has delayed the Queen's planned visit to the new headquarters of the Metropolitan Police.

A Buckingham Palace spokesman said the decision had been taken to postpone the Queen's engagement in light of the attack.

Stories of heroism and bravery emerged from the incident, which brought central London to a standstill and closed transport networks around the capital shortly after 2.30pm on Wednesday.

Paramedics fought to save Mr Palmer'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.

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.

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.

In pictures: Westminster attack Show all 9 1 /9 In pictures: Westminster attack In pictures: Westminster attack An air ambulance lands after gunfire sounds were heard close to the Palace of Westminster in London PA wire In pictures: Westminster attack MPs wait until the situation is under control in Westminster. 'The alleged assailant was shot by armed police,' David Lidington, leader of the House of Commons, told the house. BBC News In pictures: Westminster attack Crowds gather in Westminster after shooting incident, which police are treating as terror attack BBC News In pictures: Westminster attack Police were also called to an incident on Westminster Bridge nearby AP In pictures: Westminster attack Early reports indicate the car, which mounted the pavement on Westminster Bridge and mowed into around a dozen people, was the same vehicle which then rammed into the railings of the Palace of Westminster, just around the corner Reuters In pictures: Westminster attack Security sources described the suspected assailant as a middle-aged Asian man, who is understood to have left the car before attacking a police officer with a seven-to-eight inch knife PA wire In pictures: Westminster attack Police have asked people to avoid the immediate area to allow emergency services to deal with the ongoing incident AP In pictures: Westminster attack One woman has died and a number of others, including the police officer, have been hurt, according to a junior doctor at St Thomas' Hospital Reuters In pictures: Westminster attack At least three gun shots were heard by those inside Westminster, and proceedings in the House of Commons have been suspended AP

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.

A party of French schoolchildren were among those targeted on the bridge, while four students from Edge Hill University in Ormskirk were also hurt - two described as “walking wounded”, and another couple said to have minor injuries.

Romanian and South Korean tourists were also caught up in the tragedy.