I don't think that's quite right, Heathfield.
I I R C, it's actually +10% and -15%. (approx 253 to 195V), though the extremes would be exceptionally rare.
Before I retired, I used to work in the design dept of a major gas boiler manufacturer, and we had to design the boilers to operate on 230V, and work safely thru' the range quoted -- and be safe (tho perhaps inoperative) even below that.