afaik.
generally, there are no import duties at all between EC member countries.
assuming the aircraft came from say, the USA to the EC when new, then import duty will have been paid then, and there is no need to pay the duty again.
vat is another matter. think you pay either the french vat or the uk vat. again assuming, its a purchase from a registered vat seller.
fairly certain that no vat is required if the vendor is a private seller.
i stand to be corrected by anyone with more specific knowledge.