Police measures will tighten in London in the wake of the terror attack
The special soldiers will be placed on standby permanently at a secret location in the centre of the capital for at least one year.
The measures come after the terror attack when four people were killed by Khalid Masood on Wednesday outside the Houses of Parliament.
Other new security measures to try and ensure the safety of people in London include a new ring of steel around certain key London landmarks such as Buckingham Palace.
The lack of security surrounding Parliament has been criticised
No system is perfect but it’s important that any perceived weaknesses are addressed
New fencing has already been installed at the royal palace, located less than a mile of Westminster Bridge, where Masood ploughed into a crowd of people.
Cabinet ministers will also get SAS training, all police guarding iconic sites will be armed and MI5 is increasing its recruitment drive so they can monitor potential lone-wolf terrorists.
A security source said: “Incidents such as last Wednesday’s attack always highlight weaknesses in any security system.
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
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Police surveillance of the capital is set to increase
“No system is perfect but it’s important that any perceived weaknesses are addressed. People need to know how to react in an emergency.”
The SAS officers will train MPs so they know how best to react in case of a terror attack.
The elite troops will have the ability to enter buildings using explosives or even ‘fast ropes’ from helicopters to access roofs.
The new tactics will also include plain-clothes armed police officers protecting major London landmarks.
A security source said: “This is not the first time that a terrorist who was on MI5’s radar has carried out a criminal act.
“At the moment MI5 are working 24/7 trying to establish whether this attack is a one off or the first part of a wider plan.”
Acting Deputy Commissioner, Mark Rowley, said: “More widely-the police service will sustain an enhanced armed and unarmed presence over the next few days.
“London and the UK are open for business, and we are out there in greater numbers to make sure that the public see a highly visible presence help reassure them as they go about their daily lives.”
Former Met Police commander Kevin Hurley has criticised the lack of tight security around Parliament.
Mr Hurley said: “It almost beggars belief that a uniformed constable at the front gate of Parliament should be performing his duties when not even armed with a pistol.
“When suicide attacker starts, you have to stop him instantly. We have seen what a relatively unfit terrorist can do with a knife and car.
"Imagine if three fit young terrorists armed with AK47s had attacked Parliament. There would have been a very large number of casualties.”