There are 3 stages in Covent Garden.
Blue(West Piazza-in front of St Paul's Church): Where the non-musicians perform
Yellow (South Hall or Courtyard): Where musicians perform
Green(North Hall) : Both musicians and non-musicians perform; where auditions for musicians are held
The area inside the red dots is private property and managed by private management company that grants performers their license. Anybody performing even 1 meter outside is in the jurisdiction of Westminster Council. The color and the alignment of stones on the road signals where the private starts and where the public ends.
I was informed that when a homeless person causes trouble inside this area, the security just starts standing close to the person so that he/she could slowly move away with his/her own will. There is no physical contact or verbal abuse but just standing still so that the person steps out of this zone. And as soon as s/he crosses goes beyond the private property, "it's Westminster's problem".