IIRC, the use of "Pan" and "Mayday" in UK is also to cover against any claims by third parties. I once had a medical emergency on board and requested a priority landing. The controller advised that he couldn't give me that. "Pan, pan, pan"...."You are cleared direct three-mile final". That way, if anyone, e.g. people under a non-standard flight path, complain, the controller and the airport authority are covered. Different from America, and perhaps American pilots operating into UK should know about it. Thread drift; sorry.