I can't remember exact figures off the top of my head but IIRC our entire nuclear arsenal could make something like 1.6% of the Russian landmass uninhabitable (obviously would be utilised against strategic targets) while they could turn every inch of the UK to glass 1000 times over.
Each trident missile carries 16 individually targeted warheads and each sub carries 8 missiles so that means thats 128 targets per submarine (and we have 4 subs). I'm not sure on the yield of each warhead but that is a lot of destruction potential. Easily enough to threaten every major population center and military base in Russia.