According to the BBC:
"The car was previously owned by my good friend Kenny Baker who was R2D2," said Prowse.
"He used to keep a little ladder inside the boot so he could climb up and put his suitcases inside.
"When he had finished, he'd put the ladder back and used a cord to shut the boot. "I decided to leave the cord there as a reminder of the car's previous owner." Okay then.
Prowse eventually made it to his destination, a reunion of the 501st UK Garrison, which is a charitable group of people who like to dress up in Star Wars costumes.
"I'm the Commander in Chief Worldwide so it was really important that I was there, and when I broke down my boot was full of memorabilia and photos," Prowse explained.
The picture is of an unrelated car, but it seemed fitting.