I accept that the situation in a public area is more complex, and I imagine it would be very hard to get the police to act unless some substantial disturbance was being caused.

However, I live in a flat on private property. If people are there without due reason, and perticularly if they are gathered in the stairwell outside my flat smoking pot and drinking, then I think it is entirely reasonable to call the police. I wonder what the reverend would do if they were gathered in his garden - sing hymns??