Following further research the procedure for requesting permission is relatively straightforward. Lead time is 28 days and sure the outcome is uncertain but given the nature and activity of the organisation that has requested aerial footage I'm pretty confident it's worth a shot.
So the procedure for applying for a ENSF ( Enhanced Non Standard Flight ) is through NATS as laid out in IAIP ENR 1.1 paragraph 4.1.6
Non Standard Flight Applications : NATS -
Non-Standard Flight Applications | NATS
Sure I'll let you know how we get on.