A MAJOR security alert is underway at Parliament after two men and a police officer were reportedly shot just outside the building this afternoon. 

Police have locked down Parliament following the attack and witnesses also say that a car mowed down at least half a dozen pedestrians on Westminster Bridge before crashing into the gates outside Portcullis House.

MP Andrew Murrison said: "We are currently in lock down in the building adjacent to the House of Commons.

"None of us are being allowed to move understandably but it is all pretty calm in here and the police seem to be on top of things.

"In my 16 years in office I have never come across anything like this.

"I found out about this just minutes ago, just after we had done a vote in the House of Commons. 

"It is quite extraordinary and all happened very fast. Within the last hour I was at that very spot by Portillo House."

More to follow.