Sue
Hi,
I have made use of the small claims system 18 -25 times (lost count) won every time. It is a great way to bring company's and individuals to take heed of agreements.
Having won your case and if he does not pay ask the court baliff to sezie the aircraft (you get a warm feeling - I promise).
Don't do anything daft like burning up his fuel or preventing it from being moved.
All the best