Theresa May is to chair emergency Cobra meeting
The Cobra committee brings together government ministers with senior officials of the emergency services and security and intelligence agencies.
Meeting in a briefing room of the Cabinet Office on Whitehall, Cobra co-ordinates the high-level response to serious incidents, and has previously gathered after terrorist atrocities including the July 7 attacks on the London transport network and the murder of soldier Lee Rigby.
There was no immediate information on who will attend Wednesday's meeting.
May was evacuated from the scene of today's terror attack at high speed in a silver police car
Mrs May – who was within a few hundred feet of the scene – was bundled into a Jaguar which then left "at extreme speed" as gunfire rang out at Parliament during the incident.
A Downing Street source said Mrs May was safe after the attack.