The UK and Ireland are the only countries I know of where most houses have a cooker switch. Personally I've never turned one on or off ... nor would I. Whether changing or repairing the cooker, I would always turn it off at the consumer unit. I would never consider it safe to work on a cooker just by turning it off at the cooker switch. They may have had some purpose back in the day of fuses, but what purpose do they serve nowadays? Is there any requirement to install one or would my new kitchen installation be legitimate without one?