Did a week snowboarding in Val D'Isere about 10 years ago, warmest it got all week was about -18c, the coldest day was between -30c and -33c all day long!
And on that coldest day, there was a bit of a storm for an hour or so too, we were on a chairlift when it started and the winds picked up to what I'm reliably told was approximately a 30 degree windchill factor! So it was like being in -60c ambient!!!
Fortunately we weren't far from a mountain restaurant, so we got there as quickly as possible and had a lengthy lunch waiting for the storm to pass…
The upside to the seriously cold temperatures was the every morning for the entire week there was fresh powder snow everywhere… One morning there was over 15" of virgin snow greeting us!
Coldest I've been in the UK though was about -15… Don't think it's been colder than -8c here in Worcester at all today.