I'd recommend Autoglym's Screen wash, expensive stuff in a small bottle but was on sale the other day at 2.50, I bought a bottle almost a year ago and still haven't run out, and I've headlight washers too. Never freeze even after the weather in the past while plummeting to -7. It'll also literally clean anything off the windscreen. 

On 02/03/2018 at 13:58, HarleQuinn said:

 

I'm only in the West Midlands so no lower than -6c and that is rare. I do have 25% off at Halfords but is the Halfords stuff even that good? Bearing in mind I think I have the fan jet on my car too.

 

Really I am being wary of the fan jet/hoses blocking due to cheap, thicker screen wash.

 

I use the Halfords -20 screen wash and in this weather  mix it 50:50 and mine have never frozen up yet on this car or previous cars even with headlamp wash.

 

The choice of screen wash is a big factor.