As a fully qualified, certified and time-served electrician, I agree with Buildersmate. It's only a low wattage device and more than OK to go on the lighting circuit. The lighting circuit could be wired in cable as small as 1.0mm but even this is OK for such a low wattage device.
Having said that, I'd probably take the supply from the lighting circuit but via an FCU (fused connection unit) with a 3A fuse in - this satisfies the "regs" requirement for a suitable point of isolation for maintenance purposes. It means you can safely isolate it without having to turn the lighting circuit off at the CU.