Speaking as a retired Heathrow ATCO I thought it was ridiculous at the time when Police routine operations were upgraded from Cat Z to CAT B a few years ago. This does put controllers in a very difficult situation but I think breaking off traffic established in the late stages of an approach is frankly wrong and potentially dangerous both from the aircraft's and the ATC situation point of view. If the Police helicopter is responding to a really urgent situation then he has the option to declare a Police Emergency and is automatically upgraded to Cat A. Everybody then knows where they stand and an airshow can be justified.