Tell me to shut up if you know this already but be aware that the guitar and shipping costs are both liable to duty and VAT if you import the guitar into the UK from the USA. I don't know the exact percentage for guitars but typically the duty is around 6%. You pay 17.5% VAT on the lot, including the duty! This means you need to add about 25% of the guitars value including shipping to the price you will end up paying.
Just as an example, say the guitar is $3500 and shipping is $100. That's about £2020, which sounds good. However, add import duty and VAT and it's about £2530, and that's without adding any fees for actually paying the duty and VAT from the carrier.
I'm not saying don't do it. Just make sure you cover yourself the best you can and see what other options you have. For me personally I would rather pay an extra £200 extra on top of this and get a UK sourced one from a proper shop with no risk of your money going walkies. You might even get £200 knocked off a £2750 guitar if you're a wheeler dealer.