prices everything in dollars, there's an option for you to select the UK site, and there's a clear warning that "UK VAT applied to all applicable orders. All other local taxes not included." Import duty, which is the responsibility of the purchaser, not the seller, is payable on all imported goods.
Crucial probably comes in for more praise than any other company in our forum, and I don't think I can recall ever seeing a complaint about this particular problem with them before. Most people seem to find the UK site pretty easily, and I think you'll just have to put this one down to experience and pay Fedex, who have paid the duty on your behalf.