Mark Rowley, the Counter-terrorism chief, says one policeman, three civilians and the attacker died. Healso states that 40 people were wounded.
The assailant has not been identified. Rowley said police think they know the identity of the man but would not reveal details. He said Islamic extremism is suspected in the attack.
He identified the police officer who died as Keith Palmer, 48.
As it was reported earlier, incident with shooting occurred at UK Parliament building on Wednesday. A vehicle drove into a crowd at Westminster bridge, injuring several people. Then a person armed with a knife attacked police in the grounds of the Houses of Parliament, stabbing a policemen and was shot in the end.