Sharpshot
The avgas price at SEN is currently 89.06p per litre from the bowser.
If you have a card for the self-refuel facility, there is a reduction of 3p a litre with the Southend Airport card, not sure what the discount is with an Air BP card.
Fuel drawback can be claimed for flights landing abroad. I believe the FBO staff are able to take the drawback off your total for you, under an agreement with Customs & Excise to do so.