I guess there's winter & winter.
If we are talking most of the UK (eg excluding Highlands etc) , most of the time; that's very different to Cairngorm in full Arctic mode.
For 'UK most of the time', that's something like kit needed to cope with down to minus 5 degrees.
I use my normal 3 season tent, Mountain Equipment 'thick' blow up mat with old carri-mat on top. My 3 season down Alpkit sleeping bag is cosy to just below zero, if its going to be much colder I add thin summer bag on the outside or a silk liner on the inside. Take a down jacket and a wooly hat etc. I also have a Petzl headtorch with various settings. If its appropriate, a fire is great comfort / entertainment, add single malt as required. You are right that passing the time in the dark is a key issue, selecting a night when it isn't going the rain is a big help, I prefer to sit out (sometimes in the bag on the mat), rather than hide away bored in the tent, until I'm actually ready for sleep.
I keep cooking simple with my 'normal' gas canister stove. Even at zero degrees the performance of the stove is reduced; so keep the gas bottle in the sleeping bag, put it inside the down jacket before you use it etc
Camping on snow / high / really cold should probably come after some experience of all the above - sorry, I guess you already know that.