First things:
Obviously you will have to be IFR
You will need a non-standard Flight Authorisation from Terminal Control operations. (Your Operations department should be able to do that for you). They will tell you all the hoops that you have to jump through.
You can apply to the AUS for a flight priority status if you feel you need one. (Cat Z probably)
You then phone on the day for final authorisation.
You then pitch up and can still be refused if the traffic is busy.
It depends on the type of task/aircraft type/time on task etc etc.
With respect, the fact that you are planning to be
"London at 10 to 15000 feet Outside Class A airspace, say over Biggin that can be arranged "on the day" " shows a lack of understanding. NSF's with much higher priority create a huge workload and needs top class pilots on the ball in the most complex TMA in the world.
Still fancy applying!?!?!?
