Russia is definitely a danger to the UK. They have the nuclear firepower to destroy us if they choose to. We could retaliate with a single nuclear-armed submarine.
It's not likely it would get to that stage though because even Putin knows nuking a NATO country would result in a retaliation from the whole of NATO.
Cyber attacks are more likely, in fact they're a constant danger already. Expect infrastructure like power, communications, travel and banking to be hit suddenly from time to time.
I don't think Putin wants a war with the whole of Europe, he just wants to recover the territory Russia lost when the USSR collapsed. Once he's got Ukraine he'll be moving to reclaim other countries - Latvia, Lithuania, Estonia, Poland, Czechia, Slovakia, Hungary, Romania, Moldova, Bulgaria and the former Yugoslavia. Not necessarily to conquer them but to install pro-Russian governments.
That's where the risk to the UK really ramps up. If he attacks a NATO member, we'll be expected to send troops in. Hopefully it will just be a conventional war on mainland Europe so won't affect us too much. There's a risk it will become a total war of course, with Russia bombing the UK (and the US probably, from the far east of Russia) and vice-versa, and that could escalate into a nuclear apocalypse, but that's probably months, if not years away.