I think if there was a significant increase in danger by driving in mild winters * with summer tyres, it would a legal requirement to switch to winter tyres, as it is in many parts of Northern Europe. Who knows, it might become a legal requirement in the UK but I doubt it ever will. E.g. it's a legal requirement in Poland where I spend a lot of time but it is so much colder there and you're guaranteed a lot of snow every winter. Even their airports work in the snow!
* I'm thinking south of England here, I might get them or at least consider them if I lived in Scotland and regularly saw snow. If you ignore the last couple of winters, I used to see maybe one day of snow a year and it was all gone a day later.
I also take your point on early morning driving and appreciate you'll see more ice but I don't think a 7% improvement in stopping distance is a good enough reason. You could get a much better safety margin by just driving more slowly in freezing conditions IMO