5,000 soldiers ready to back up police amid fears the Met is unable to maintain current security
The Met has increased its number of armed officers, but is still 600 short of its target number.
However, thousands of troops are ready to step in if needed.
After Wednesday’s terror attack on Parliament, police are on the alert for follow-up assaults or copycat killers.
Of particular concern is a warning from MI5 that unarmed police could be drawn to what seems a minor incident and find themselves ambushed before they can call for back-up.
Operation Temperer, signed off by Defence Secretary Sir Michael Fallon 18 months ago, provides for up to 5,100 troops to be on standby.
Troops would be drawn from 16 Air Assault Brigade in Colchester and the Plymouth-based 3 Commando Brigade.
Brigadiers from both have attended top secret meetings at the Ministry of Defence to ensure troops are ready to deploy.
Armed soldiers would enhance security in key areas and release police resources from duties such as guarding public buildings and transport hubs.
We can call on the support of the military, should we need to
Mark Rowley, Met Police
They would be escorted by unarmed police officers. A new 70-strong SAS unit was also on standby last night with seven police liaison officers.
It will use helicopters based at three key military airfields and two provincial airports to react swiftly to attacks outside London.
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Special Forces soldiers attached to the Police Counter Terrorist Command spearheaded the response at the House of Commons on Wednesday, minutes after a code red alert was triggered.
Despite increasing the number of armed officers the force is still 600 short of its target
The team, officially listed as military liaison officers, have operated with the CTC for the past two years as part of a wider plan to ensure the SAS understands police procedure and the logistics of operating in London.
They joined officers from the CTC who formed an immediate response at Westminster wearing grey suits, face shields, helmets and carrying stun grenades and automatic weapons.
Troops would operate only under the direction and control of the police.
Britain has a total of 7,000 police firearms officers.
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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
In January last year Met Police assistant commissioner Mark Rowley obtained permission to double the number of its armed officers to 2,800.
But the force is still 600 officers below target.
Mr Rowley confirmed: “We can call on the support of the military, should we need to.”
Last night the Ministry of Defence’s new Joint Cyber Unit led by MI5 was facing its first major civilian test as it helped police and intelligence analysts in the hunt for a possible terrorist network.
MI5 have warned that police may be drawn to what appear to be minor incidents before being attacked
The move comes after counter terrorist officers arrested members of Westminister killer Khalid Masood’s family and recovered a wealth of computer files, which have provided new leads to the killer’s lifestyle.
As detectives trace his past through national insurance numbers, social network and friends, the small military cyber unit is working with GCHQ and the Home Office to establish whether or not Masood was a lone wolf.
Formed in the past couple of years, the unit includes army, navy and air force personnel who are based at MoD Corsham, Wiltshire.
Using counter-terror skills honed in Afghanistan, where electronic warfare specialists monitored Taliban communications and tracked mobile phone signals, the unit is tracking suspects, searching for code names of extremists and seeking to identify regular visitors to extremist web sites.
A senior source said: “Cyber operations are a key aspect of modern warfare.”