Although they are available for helicopters, I'd be very surprised if one was fitted. Flying through London I suspect there would be many false positives - to such an extent a pilot may well turn it off anyway.
Many, if not most, modern corporate helicopters do have TCAS, or similar fitted. I'm not sure what you consider a "false positive". I can assure you that professional helicopter pilots flying in CAS do not turn it off, and certainly not over London.