if it's an old boat that didnt have VAT paid on it in the EU (maybe imported without paying, or never paid when sold originally)....
-as far as I know if its pre-1985 theres no liability.
-if there is VAT liability, I believe it's due not on the price you pay, but either on the original price, or the modern day equivalent new price - double check.
All of the above (and below) is just heresay, ask the VAT man directly to be sure!
Johns: Need more info. New or 2nd hand? Why is it not VAT paid already? Why do you think the 25k will not include VAT? If VAT becomes payable now, it will be on the value of the boat, not it's original price or it's modern day equiv price. Except that in Spain they assess VATable value using depn tables, so they usually charge VAT on a bit less than the true value
If you ask UK Inland Revenue/Custom for VAT advice on this type of stuff, treat the answer with extreme caution imho. This is complex and most people who really understand tax law dont work in Customs/Revenue call centres. The call centre person will likely answer your question, but there's a high risk the answer will be wrong and you might even ask the worng question slightly, and you can't hold them to that wrong answer, so it can be worse than useless
From your question it sounds like you already know that VAT is due so I won't go on about the criteria that would determine its VAT status.
The answer, therefore, is that to pay VAT in Spain will be very much cheaper than paying it in the UK.
If your boat is known to the Spanish in general, it will most likely have a "value" as deemed by customs, set out in (as I understand it) the Bulletin which sets out various makes of boat and states their Customs value. VAT would then be payable on that figure at the most at 16% (I did hear 8% from a broker once but that may not be guaranteed!).
If your boat is not in the Bulletin (for instance I don't think Westerlys are) you would need the Customs to value it for VAT purposes..... however unless the boat you have bought was a total bargain, the figure they will come up with, will more than likely, be a fair bit less that its actual value, as for the most part anything to do with taxes in Spain means "declared values" and not real values as the Spanish have made paying the least tax possible into an art form!
Declared values often have 20% (sometimes much more) off the actual value. I believe there is an English lawyer in Mallorca who does VAT on boats, if dealing with Spanish customs is too frightening.
In UK you would expect to have to pay 17.5% on either the bill of sale price, or have the UK Customs valuing your boat to what they think it is worth, and they might think its worth more!
Regarding moving it - you don't say how long it is. However a 33ft was moved Denia to UK for £2.5k. What you should think about are all the lorries going back empty from around the Port Leucate region of France after playboys toys have been brought to the Med. THe closer you can get your boat to Port Leucate the cheaper you may find transport!
If its pre 1st Jan 1985, (but after 1st April 1973) you still have to prove its exempt, by it having been in the EU on 31 Dec 1992, if you can't proves its exempt there is a VAT liabilty.
THe liabilty will be either what the Customs officer deems its current value to be, or the current Bill of Sale price.