We get minus 15 to minus 20 here most winters. We mix screen wash at about 50/50 or more in cold water, as cold as you can get. Works down to minus 9 so far. If snow is on the ground, we only do downstairs at about half price. Got that tip off here a couple of years back off some crossdresser called Matt.
If you work below minus 4 and use warm or hot water, it freezes on contact here. Not sure about UK, but mainland Europe has less humidity or something at low temps. That's what I think some expert explained on here last year.
In most of UK, you only get an average of minus 2 or 3 most of the winter, so you should be OK.