Falconpilot. If you say 'Medical Flight' going into the London TMA, you will receive no priority at all, just the same as if you say we have a'VIP' onboard. No Priority.
If you are carrying human organs etc, if you consider it is 'urgent' that you need to be on the ground ASAP, then call PAN and we will not question it, you will have No Delay.
If in doubt, tell us in plain English and everything possible will be done for you.
However, please tell us as soon as you know you need a priority approach so that we can plan around it.
I would much rather be told when you are lots of miles out than when you are at the top of a stack, having just been given a 15 min delay.
Sometimes the info does not get through properly, so if you enter a 'new country' (Air Traffic Control Centre), makes sure your requiements are known. This may even mean getting your Company to phone TC.