Hi,
I have gone many years without problem, but recently the light switch in a room has started to smell strongly of ozone, the 'electrical smell'. This has never happened before and I'm rather worried. The switch also produces a buzzing noise that coincides with a flickering from the light bulb, which is an energy-saving fluorescent bulb. I have no filament bulbs to hand to check if the type of bulb is the problem. Also, the smell continues even when the switch is fully off.

Thanks for any advice.

Replace the switch immediately if you have confirmed all wires are securely attached. The smell and flickering indicate arcing which could be inside the switch