Be careful with this if you put on different wheels. E.g. I'm with QuoteMeHappy.com (Aviva's online only offering). They are happy with winter tyres but I'd have to get their OK to switch to steel rims.
"At Quotemehappy.com, we’ll let you change your tyres to winter tyres as long as the new tyres are the same profile and size as the tyres that are currently fitted to your car
For example if you have steel wheels currently fitted, then you can change the tyres to winter tyres. But you can’t change the wheel to an alloy wheel."
So if I took off the 17" alloys with 195 45 R17 tyres and put on 16" steelies with 195 50 R16 tyres that would be a modification which would need to be declared.