Their deployment is aimed at preventing another attack like those in Manchester and on London Bridge in recent weeks, a source told the Daily Mirror newspaper.
"The view is there are so many homeless people out there undercover operators will remain safe and anonymous," the unnamed military source told the newspaper.Another military source told the Mirror
"Anyone trying to pick on them would be extremely foolish and the public should feel reassured that a lot is being done to minimize the effect of another attack."
"The armed units have been deployed for some time now and it is unlikely the operation will be brought to a halt.The SAS were pictured deployed alongside police in the operations following recent attacks and conventional troops were deployed around major buildings including Parliament.
"The threat level is still assessed by the Joint Terrorism Analysis Center as severe and that means an attack is highly likely so we must be ready."
The SAS has long performed non-uniformed roles as part of counter-terrorist operations, including in Northern Ireland, though part of the reconnaissance and observation workload has now passed to the more recently formed Special Reconnaissance Regiment (SRR).
The troops posing as homeless people are reportedly armed with Heckler and Koch MP7 submachine guns and fed by other soldiers dressed as civilians, who hand them food on a rotating basis under the guise of charitable passersby.
The Mirror reports they are mainly drawn from G Squadron, 22 SAS regiment, and the unit's Counter Revolutionary Warfare wing.
Have you ever read such evil in your entire life? Proves beyond any doubt that the system is entirely criminal and savage.
Homeless are SAS Troops.? If you believe that you will believe anything.