I saw on the news last night that Europe is getting slammed with one of the worst winters in over a century. hundreds of people have died. Hope it's not that bad in the UK, and glad I'm not there.
Chickens can take a lot of cold, as long as their coop is dry and draft free. The big concern is frostbite and infection.
Give them lots of bedding. You can rub their waddles and combs with vaseline or something similar, to protect them from condensation, and freezing.
If you have electricity available to the coop, you can consider adding some supplemental heat. Lots of options there.
Good luck & stay warm,
Imp