Yes.
You are supposed to clear the snow and ice off your window first, its a legal requirement
@Eric (section 41D of the Road Traffic Act 1988).
I live in Scotland too, i don't have heated screen washers (or a heated screen) on my Defender and i've never had that issue, ever.
It did get cold enough to feeze my skushers a few yearsa ago but to be honest that was my fault as I still had summer mix in the bottle.
If you turn on the heated windscreen (I think only standard on the Fieldmaster ?) or direct the aircon at the windscreen then you will find that the heated screen washers offer a huge advantage of non heated as you can skush almost immediatly whereas in my old Defender it takes a while for the engines heat to melt the fluid in the pipes and jets.