If its just a kit try DHL. If its a plane in a crate you probably are better off to contact a freight forwarder. Check the phonebook. It may take several calls but you'll probably find one that has more shipments to the UK and therefore has better rates. Also check with the person to whom you are shipping. They may be able to find a forwarder on their end easier and arrange it where you just drop it off at a certain location near you. If you do it that way it may be easier on the person receiving for clearing customs and the duties involved.
Thats how I had something arranged that went to Saudi.
Mark