Great question - both extremes for me are rather odd.
Lowest - 1°C, in the bathroom of an old, draughty unheated attic apartment in Buxton, Derbyshire in March 2018 (BftE). Yes the bath froze up and was unusable. Only heating was an electric space heater in the main room.
Highest - 33°C in the kitchen of the same apartment - in December 2017. I had a horrible old electric cooker in the small kitchen, one evening a loose knob on the front of it got knocked inadvertently, and it switched on over night, heating up the whole kitchen. I walked in late next morning to a wall of heat in the room, and the smell and sight of a nearby plastic bag beginning to melt and smoulder. It was my fault for not turning the cooker off at the wall, given it had cranky loose knobs on the front of it that could be easily knocked on.