Shocking new footage has revealed that the gates into the Houses of Parliament were open and unmanned for several minutes in the aftermath of Wednesday's terror attack.
The video, captured by The Times, sees armed officers swarming the forecourt following the terror attack but leaving the iron gate that allows in vehicles wide open for several minutes.
The latest revelation has raised fresh questions that the terror carnage would have been even worse had the terrorist, Khalid Masood, been joined by an accompolice.
In the video, pedestrians can be seen walking past the wide-open gates following the terrorist attack, leaving the iconic political site open to a potential second attack.
Shocking footage has revealed the gates into the Houses of Parliament were open and unmanned
At one stage during the brief security lapse, a courier on a moped even appears to enter the grounds unchallenged.
Metres from the scene, at the same time, Theresa May was rushed from the scene in a waiting car.
Following the attack, MPs have called for a review of the security arrangement around Parliament.
Despite this, Scotland Yard's anti-terror chief has insisted that current arrangements are "proportionate".
The last photograph of PC Keith Palmer, 45 minutes before his tragic death
Our current arrangements have been developed with Parliament over many years and are designed to provide access to the seat of our government balanced with security that is proportionate but not overly intrusive
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Mark Rowley said that procedures for keeping Parliament safe had been designed so they were not "overly intrusive".
He said: "Our current arrangements have been developed with Parliament over many years and are designed to provide access to the seat of our government balanced with security that is proportionate but not overly intrusive."
Parliament's main entrance has two sets of large metal gates which allow vehicles to enter and exit the estate.
A pair of smaller gates were introduced recently with two police officers at each to check passes and allow cyclists, cars and delivery drivers to come in.
There are usually armed police present just inside the entrance gate.
More armed police are also present after the final checkpoint.
The latest revelation has raised fresh questions that the terror carnage would have been even worse London terror attack: Latest pictures Fri, March 24, 2017
4 dead and 40 injured in London terror attack
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Armoured police personnel carriers are seen on a street leading to the Houses of Parliament in central London on March 24, 2017 two days after the March 22 terror attack on the British parliament and Westminster Bridge
She said: "The one weak spot on our estate is those Carriage Gates. We have four police officers there. Two on the gate going in, two on the gate going out.
"We see them every day, we’re friends with lots of them. I think we will need to look at security at the Palace in the wake of this incident but this is a plan for another day. It’s a terrible, terrible day for Parliament.”
"It’s a terrible, terrible day for Parliament."
Former Met firearms officer Roger Gay said Britain may now need to move away from the idea of unarmed policeman in important locations.
He told Sky News: "In my opinion, I would have all of them in that location, I think, should be armed. What you have there, and I hate to use the term, is perhaps a sacrificial pawn.
"But one wonders if he had a sidearm, would he have been able to react that quickly and, if he had been carrying a carbine then he would be less of the traditional policeman. Perhaps we should let go of that and ratchet it up one notch.”
"Perhaps we should let go of that and ratchet it up one notch."
Former civil service Chief Lord Kerslake has also called for "a complete overhaul of security from top to bottom."