Character mistake: 27/1/15 Max tells his two daughters to get in his car to go to Emma's funeral. Max's car is a Mercedes SLK which is only a two seater, and therefore wouldn't seat three people.
Character mistake: When Pat goes to Roy Evans' car showroom to complain about the dodgy car he sold to her son David, she asks Roy if he has any children. Roy replies that he has two sons which was true, but at this time Roy didn't know he had a second son, Nathan, conceived years before when Roy had an affair with his secretary Doreen. He only found out years later when Nathan turned up to tell Roy that Doreen was terminally ill. When Roy was speaking to Pat he only knew about his first son and business partner Barry.
Answer: Most likely a mistake by the set designers or it's a recycled set which already had the switch on (they just repaint and add other fittings).
At my workplace there is a two-gang switch with a three-gang switch underneath it, one of which is for the shop lights, the other four have no apparent use.