It seems to me to be massive overhill to be paying a policeman's wage to infiltrate a gang of half a dozen dozy racists. Especially when anything they do, holding meetings or beating up Daryan, they are surrounded by Street residents who can identify them straight away.
They should know you get anyway with nothing on that street, even Stephen is going to be found out sooner or later. Presumably he will start to unwind when Audrey tries to release equity to help Nick buy Debbie's share of the bistro. Incidentally, when I released equity, it involved several people and a face to face meeting with a lawyer, not a quick phone call.