There are some strange answers in this thread.
Firstly, the original poster, apparently being a novice pilot, should plan for the lowest workload and the greatest probability of being able to fly the route he planned, and that means planning it outside controlled airspace. Because VFR flight does not come with any sort of enroute clearance (neither does IFR flight outside the airways system, for that matter) you have to ask for a transit from every piece of Class D, and since they can refuse you have to plan the flight outside CAS anyway....
Planning the route on VORs gives a highly desirable companion to visual navigation... as would a decent GPS of course.
Regarding duty drawback, yes you can claim back drawback (approx 28p in the pound) for all fuel exported from the UK i.e. all fuel carried on a flight which terminates in a non-UK landing. Under current regs, even if some of the fuel on which drawback was claimed is still in the tank upon return, or if most of the fuel consumed was actually consumed within UK airspace, you can still claim back the whole lot as described. A lot of people think this is overly generous and "must" be wrong, and some Customs officers have given advice that differs, but this is the current legislation!
What you cannot do is claim back the duty twice on the same fuel, obviously, and Customs have arranged their application forms so as to make it more apparent if somebody did that. It is quite likely to be done accidentally on a club plane where nobody knows or cares where the previous renter took it. Obviously this leads us to the ethical issue of who should keep the drawback; if you claim it and still leave half a tank in there, then the next person can't claim it and you in effect got a cheaper trip than he is going to get. When I used to rent mine out, one person (an instructor!!) flew to L2K, claimed back the drawback on 240kg of a full tank, pocketed the lot, and the drawback paid for his entire fuel bill there and back! Of course it meant that one had to make sure that the 80% of the tank which he came back with had to be used up in the UK, which was a little unfair on myself or subsequent renters. I changed the rules after that, into a straight discount to anybody going abroad, and that was fair to all. The degree to which different clubs care about this varies, but do check with the body you are renting from before claiming the drawback and pocketing the lot.
Regards VAT, this is more complicated. I know of one airfield that sells VAT free fuel if your stated destination is overseas. I have no idea if this is legal. In normal export (goods/services) one does not charge VAT, unless the customer is in the EU but cannot supply his VAT number in which case you do have to change VAT... I have never heard of claiming back VAT on exported fuel.