Andrew Ainsworth sculpted the white helmets worn by the sinister galactic warriors in the original 1977 film, and now sells replica costumes, made from the original molds, over the Internet.
Lucasfilm Ltd. has been trying for years to stop him, in a battle that has climbed through the British courts.
Lucasfilm's lawyers argued that the suits are works of art and therefore covered by copyright law.
The country's highest court ruled Wednesday that the costumes were just props and covered by a shorter copyright period, which has expired.
Ainsworth may now make and sell replicas of the helmets, but only in the U.K.
The Associated Press contributed to this report.