314.4 - Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energising of a final circuit intended to be isolated.
Building regs state as follows: Cooker control switches, extractor fan switches, etc, should not be mounted so that it is necessary to lean or reach over gas or electric hobs for their operation.
Think about it - a pan fire starts and the switch is behind the pan that is on fire. Common sense I would have thought.