The policeman stabbed to death in the grounds of the Palace of Westminster has been named as husband and father Keith Palmer.
The 48-year-old officer had served in the Metropolitan Police Service for 15 years and was a member of the specialist parliamentary and diplomatic protection command.
He was killed on Wednesday afternoon after an attacker armed with two knives entered the gates of Parliament and stabbed him.
Speaking outside Scotland Yard, acting deputy commissioner Mark Rowley, the Met's top anti-terror officer, 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."
Tory MP James Cleverly, who said he had known Mr Palmer for 25 years, tweeted that he was "heartbroken".
Mr Rowley added that a further three police officers were among the injured, two of whom were in a serious condition.
