A rat called Robson has won the lead role in a new exhibition at a London tourist attraction.Robson saw off fierce competition to star in Rat Walk - a new feature about the role rats played in the Black Death, at the London Dungeon.He was one of six rats auditioning to co-star with the Dungeon's Rat Catcher in the exhibition, due to open in time for the Whitsun holiday.All six had acting pedigree, with ancestors including Jasper who appeared in Sweeney Todd, Ludo who scuttled around on the set of Hot Fuzz and Nancy who starred in BBC1's Sherlock.But there could be only one winner and the judges unanimously crowned Robson the top rat."Performing is at the heart of what we do and we hold regular auditions to find the best actors for the horrible character roles we have here at the London Dungeon," explained general manager Ben Sweet."But auditioning for rats is definitely a first. We do already have a family of rodents living here, but they are not performers."