Hi Luke,
and which reg says it has to be 300mm from a sink in a kitchen???
i am aware that the regs talk about equipment being suitable for their environment. if you were to mount a 13 A socket, for example, directly above a sink, it could be argued that it unsuitable, due to possible water ingress etc., but what if the socket was to a high IP code such as IP67 (capable of temporary immersion in water i believe)
appreciate this does not fully answer you, but the reason you cant find the reg is there isnt one (ar far as i am aware) - so it could be a straightfoward judgement call on your part. A pull switch would be safer than a flick switch, and a flick switch further from a source of water is safer than one closer to it (sorry if you are now sucking on something oval in shape that comes from a chicken!)
Sorry i cant help further !!!
regards
Tony