I'd be very leary of plugging your die grinder into anything that will reduce the voltage. It will more than likely overheat and burn up. I am not familiar with the HZ that the UK uses. But Inthe US. a 220V tool will run on a 110V at half speed untill it overheats and burns up. There used to be quite a lot of variable voltage construction tools out there. They were designed to be used on the older style genereators that fluctuated with load. I don't know if your grinder has this capability but it will tell you on the name plate.