VAT
If your importing an aircraft to operate in the Uk on an N reg, you will have to pay VAT (and import duty).
They make you pay this now because it will be permanantly based and used here. Sadly because the way N reg trusts work, you don't legally own the plane. A US citizen or company does, who cannot be VAT registered. So you cant claim it back as input tax if your registered.
If you put it on a G reg you can, but you would have to operate it as a business, or like me tag it on the an existing business.