Having spent 25 years living in the Angus Glens we would always swap from summer to winter tyres each spring and autumn.
We would buy as second set of alloys foir the bay and fit winter tyres. I have used Nokians mainly and they were a godsend some winters when even with 4x4 there would be no traction with summer tyres.
One year I used winters all year on my then car, a Touareg and they were fine. The tyre many=factueres say that if you only have one set of tyres for all year use, then winters are better than summers in climates where snow and ice are a factor in winter.
Now being in Lincoln, I haven't bothered fitting snow tyres but the wife's Q3 with winter tyres was needed when we had the beast from the east.
Personally, as has been said already, further south in the UK I would fit all seasons so that you lose the slight worry of those winter days when ice and slush are present, while not really reducing any driving dynamics in summer (for a non-chav, don't need to be the fastest guy in town style of driving.)