Here is the text of the Prime minister's statement on today's attack
"I have just chaired a meeting of the Government’s emergency committee, COBRA, following the sick and depraved terrorist attack on the streets of our Capital this afternoon.
"The full details of exactly what happened are still emerging. But, having been updated by police and security officials, I can confirm that this appalling incident began when a single attacker drove his vehicle into pedestrians walking across Westminster Bridge, killing two people and injuring many more, including three police officers.
"This attacker, who was armed with a knife, then ran towards Parliament where he was confronted by the police officers who keep us – and our democratic institutions – safe.Tragically, one officer was killed. The terrorist was also shot dead.
"The United Kingdom’s threat level has been set at severe for some time and this will not change. Acting Deputy Commissioner Rowley will give a further operational update later this evening.
"Our thoughts and prayers go out to all who have been affected – to the victims themselves, and their family and friends who waved their loved ones off, but will not now be welcoming them home. For those of us who were in Parliament at the time of this attack, these events provide a particular reminder of the exceptional bravery of our police and security services who risk their lives to keep us safe.
"Once again today, these exceptional men and women ran towards the danger even as they encouraged others to move the other way. On behalf of the whole country, I want to pay tribute to them – and to all our emergency services – for the work they have been doing to reassure the public and bring security back to the streets of our Capital City. That they have lost one of their own in today’s attack only makes their calmness and professionalism under pressure all the more remarkable.
"The location of this attack was no accident. The terrorists chose to strike at the heart of our Capital City, where people of all nationalities, religions and cultures come together to celebrate the values of liberty, democracy and freedom of speech.These streets of Westminster – home to the world’s oldest Parliament – are engrained with a spirit of freedom that echoes in some of the furthest corners of the globe.
"And the values our Parliament represents – democracy, freedom, human rights, the rule of law – command the admiration and respect of free people everywhere. That is why it is a target for those who reject those values.
"But let me make it clear today, as I have had cause to do before: any attempt to defeat those values through violence and terror is doomed to failure.
"Tomorrow 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."