I'd like to wire the shower room extractor fan from the shower pull-switch so that it goes on with the shower and not the light. I found some info where one person said it's a no-no under current wiring regs but could be done via a contactor, and another says it can be done without a contactor as long as it goes via a fused spur from the shower switch.

Any electricians here can tell me which is the legal way to do it as I'd like to do it through a fused spur from the shower pull switch for simplicity..