Drawback:
As I understand it, flights from the UK to the Continent, the Channel Isles, Ireland and Isle of Man are eligible for Drawback. This is a refund of the duty paid on fuel, and is 24.75p per litre (or thereabouts) at the moment.
You are entitled to claim the drawback on full tanks provided:
1) Your load in the aircraft permits you to depart with full tanks (and remember your 4 hours notice to customs will list the people on board, so don't fiddle it!)
2) You depart straight abroad (i.e. no customs stops or whatever on the way) with full tanks;
3) You can provide fuel receipts if required to support the claim that enough fuel has been loaded to fill the tanks since the aircraft last went abroad (i.e not necessarily only the refuelling you do just beore you depart). If the a/c goes abroad a lot and everybody is claiming their drawback then you can't have it twice. This means that if for example the a/c is just back from France and has half tanks left you can only claim for what it takes to fill it up since the refund has already been given on the first lot.
I have never been asked to produce the receipts themselves, but you do need to give receipt numbers on the form you send off. They usually send you a cheque within a couple of weeks and will also arrange for it to be paid direct to your bank on future claims if you want to.
It is worth doing: On an Aztec it's about £150 for full tanks, and on a Cherokee about £60.
Hope this helps.
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"Take-off is optional, Landing is mandatory"