Star Wars creator George Lucas's long-running battle with a British prop designer who sells replica stormtrooper outfits has reached the UK supreme court.

Twickenham-based Andrew Ainsworth, who built the original costumes from 2D drawings while working at Shepperton studios on 1977's Star Wars, has been selling the outfits online for a number of years based on his original moulds. In 2004 he sold two original stormtrooper helmets at auction for £60,000 and has since created replicas that he sells as fancy dress for up to £1,500.

Lucas maintains the designer does not own the copyright, and has taken the case before a succession of judges to halt Ainsworth's work. Jonathan Sumption QC yesterday told the supreme court it was an "implied term" of their working agreement that Ainsworth "would not be entitled to retain copyright for the artefacts".

The hearing will make a final decision as the case reaches the highest appeal court in the UK. Lucas successfully sued Ainsworth for $20m in the US when he began selling replicas of the models in 2004, but the film-maker's case was thrown out on appeal at the high court in 2008. Justice Mann concluded the costumes had a "utilitarian purpose", and were industrial props rather than "works of art" so were not covered by British copyright laws. In 2009 the ruling was upheld by Lord Justices Rix, Jacobs and Paten at the court of appeal.

Lucas is expected to cite support from fellow Hollywood behemoths Steven Spielberg, James Cameron and Peter Jackson during the case.