Search PPRuNe (or Google) for terms like Customs and Excise, or the HO60 form. It's been discussed here before.
No duty, so no drawback, on Jet-A though. Only on Avgas 100LL and mogas.
The only time I ever checked this out, about a year ago, I called HMCE about this. They posted me the HO60 form because apparently it is (was) not available online. At least not officially. And the other thing is that they can *only* post you a cheque. Cashing that cheque here in the Netherlands would have cost more than the cheque itself would be worth... They don't do bank transfers, credit your credit card, paypal or any other "modern" way of transferring money.