Alan: You don't wanna go upsetting the Mitchells, they have long memories.
Zoe: My sister is my mum. My Dad is my granddad and my uncle, and my uncle is my dad.
Frank Butcher: What do you take me for? Some kind of Donut?
Frank Butcher: What do you take me for? Some kind of Pilchard?
Zoe: This ain't the Sound of Music, he's not going to marry you.
Frank Butcher: You're a wave short of an ocean, aint ya?
Alfie: You know what they say, darlin', the course of true love never runs smooth.
Kat: I don't want smooth, just something that's less like roller-blading down the Himalayas with a rocket up me backside.
Frank Butcher: What do ya take me for? Some kind of ice cream?
Frank Butcher: I'll tell you what, pal, you talk to me like that again and you're gonna get a dry slap.
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.