I have the privelage (or sometimes the problem) of providing an Air Traffic service to the Police helis in and around the Heathrow CTZ. I have always found them to be flexible, (when possible, due to the nature of the task) professional and extremely grateful. Many are ex military pilots. They are under pressure from the units on the ground, the Air Traffic Control unit they are working, and, most of all, the guys down the back. As AlanM knows, they are always more then willing, when able, to offer those interested and affected by their operations, a trip around their ops room and a chat with the crews. Give them a call...you never know where it could lead!