Continuity mistake: 12/4/13: When Sharon claps her hands to get everyone's attention to tell them that her and Jack are not getting married, look at Kirsty - she is looking at Sharon over her right shoulder, but when the angle changes Kirsty is facing forward, and then turns her head to look at Sharon over her right shoulder again.
Other mistake: Friday 12/8/11 Greg leaves for his holiday in Mexico by taxi. After he has gone you can see his pick-up truck parked in front of Dot's car in the square. On Monday 15/8/11, Greg's truck has gone.
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.