Probably Russia will try this, but if their cyber attacks on Great Britain are as inefficient as their attempts to hack Denmark and Germany's railway controls, blow up Nordstream etc. I don't think you need to worry too much..
However, it does no harm to be prepared, so make sure you have printed copies of any and all information that is usually online (prescriptions, income tax etc. etc. an up-to-date bank balance ) and phone numbers of all the official offices you have got used to dealing with online.
Withdraw some cash at the beginning of December and put it in a safe place in your home (but not so safe a place, that, like my late mother, you cannot remember where the safe place is.)
If you have a wood-burner, order a load of logs, if calor gas heaters as back-up, make sure you have a couple of full gas bottles.
The so-called cyber experts in Russia haven't yet managed to totally incapacitate the Ukranian systems, so what makes you think they can penetrate the British?