- Five people died after a terror attack outside the Houses of Parliament.
- A vehicle hit pedestrians on Westminster Bridge.
- The suspect was among the dead as was an unarmed police officer.
- 40 others injured in the incident which police is treating as terrorism.
- Eyewitness accounts from Westminster terror attack.
- Prime minister Theresa May condemned the "cowardly" attack.
Mark Rowley said that the attacker was known to police and was believed to be inspired by international terrorism. He said that a police presence would be stepped up across the country.
The assistant deputy commissioner Mark Rowley has named the police officer who died as Keith Palmer, and the death toll has now risen to five.
There has been a big response from world leaders in condemning the attack.
US president, Donald Trump, offered his condolences during a call to the prime minister, Theresa May and pledged the "full cooperation and support of the United States government in responding to the attack and bringing those responsible to justice".
Meanwhile, the Canadian prime minister, Justin Trudeau, also condemned the attack, saying in a statement: "I was shocked and saddened to learn of the innocent people who were killed and injured as a result of this cowardly attack.
"Canada and the UK are the closest of friends and allies. Our friendship is based on shared values and history – indeed, Canada's parliament is a descendant of the chamber targeted this morning.
"Today's attack on the UK parliament is an attack on democracies around the world."
British prime minister Theresa May has described the attack as "appalling" and "sick" in a press conference outside Downing Street.
"The United Kingdom's threat level has been set at 'severe' for some time and this will not change. Our thoughts and prayers go out to all who have been affected.
"Let me make it clear today... any attempt to defeat those values through violence is doomed to failure.
"Parliament will come together as normal... and Londoners will get up and go about their day as normal... they will walk these streets, they will live their lives... never giving into terror and never allowing the voices of hate and evil to drive us apart."
In a show of solidarity, lights on the Eiffel Tower will be turned off at midnight CET (11pm GMT) after the Paris mayor Anne Hidalgo said that the cities "share a common love of freedom and an attachment to democracy".
In Israel, the Tel Aviv city hall is lit up in the colours of the Union flag.
Liberal Democrat leader Tim Farron has described the attack as more than simply an "attack on democracy", the BBC reported.
"Actually it was an attack on a hard-working copper doing his best to keep us safe - and I know up to a dozen utterly innocent people who were just going about their business."
London mayor Sadiq Khan has issued a video message of support to Londoners.
London Ambulance Service deputy director of operations, Pauline Cranmer said 12 patients have been treated for serious injuries, who were all taken to hospital. Eight further patients were treated for less serious injuries at the scene.
"We have been working closely with other members of the emergency services at the scene, with our priority being to ensure patients received the medical help they needed as quickly as possible," she said, in a statement.
The Labour leader Jeremy Corbyn has issued a statement, saying: "Today's horrific attack in Westminster has shocked the whole country. All our thoughts are with the victims of this outrage, their loved ones, families and friends.
"Those victims include civilians and police officers, Londoners and visitors, subjected to a brutal and indiscriminate assault. Our thanks and gratitude go to the police and emergency services who responded so bravely, and to those – including the MP Tobias Ellwood – who went to the aid of the injured and dying.
"This was not only an attack on innocent people. It was also an attack on our democracy. But I know that Londoners and people across the country will stand together in defence of our values and diversity."
After several hours, the lock down of Westminster seems to be over.
There were around 1000 people in Westminster Abbey, including parliament workers and MPs. They were interviewed by police to see if they had any information that could help the inquiry.
The Metropolitan police head of counter-terrorism and acting deputy commissioner, Mark Rowley has said in a statement: "We have an ongoing operation - and whilst we currently believe there was only one attacker - I am sure the public will understand us taking every precaution in locking down and searching the area as thoroughly as possible.
"I know that the officials working within Parliament and the public completely understand why we need to do this and I thank them for their patience and support."
After the death of the police officer, the Metropolitan Police are flying their flag at half-mast.
Home Secretary Amber Rudd is on her way back to London from Lahore and she said that the attack on Britain's "shared values" will "never be destroyed".
In a a statement, she said: "The British people will be united in working together to defeat those who would harm our shared values. Values of democracy, tolerance and the rule of law. Values symbolised by the Houses of Parliament. Values that will never be destroyed."
Downing Street has issued a statement, saying: "The thoughts of the PM and the government are with those killed and injured in this appalling incident, and with their families.
"The PM is being kept updated and will shortly chair COBR".
Donald Trump Jr has caused a Twitter row after sharing a six-month old interview by London's mayor with the Independent, headlined: Sadiq Khan: 'London mayor says terror attacks 'part and parcel' of living in a major city.'
It was interpreted by many as goading the London mayor, during an ongoing crisis.
IBTimes UK has produced a video of what we know so far.
Liberal Democrat leader Tim Farron spoke with journalists in Westminster, including IBTimes UK reporter Ian Silvera.
Police confirm that four people have died, including the suspected attacker.
A police officer and two people who were on Westminster Bridge when ploughed through pedestrians are also confirmed to have died.
A further 20 people have been injured after being hit by a vehicle on Westminster Bridge, including three officers.
Police do not think they is anyone else involved in the attack at this time.
Rex Tillerson, the US secretary of State, has issued a statement on the London attack.
President Donald Trump has also been informed and has spoken to Theresa May.
The BBC is reporting the stabbed police officer who MP Tobias Ellwood was previously seen attempting to resuscitate outside Parliament has since died from his injuries.
If confirmed, the policeman will be the second person to have been killed in the attack.
The French Prime Minister Bernard Cazeneuve has said a number of French students are among the casualties injured outside Parliament.
According to local media, the injured are students from the lycée Saint-Joseph de Concarneau school.
The announcement comes as world leaders have reacted to the attack in the capital this afternoon.
Tory MP Tobias Ellwood has been hailed as a hero after he tried to save the life of a policeman who was stabbed in Houses of Parliament.
He was seen attempting to give the police officer mouth-to-mouth resuscitation and stem the blood flow by applying pressure to his wounds, according to The Telegraph.
Elwood – a former soldier – lost his brother Jon in the Bali terror attack in 2002 that killed 202 people, including 27 Britons. He has been an MP for Bournemouth South since 2005 and most recently worked as parliamentary under-secretary at the Foreign Office.