Bristol always has a lot going on, very relaxed vibe, vibrant music and arts scene and generally a very friendly city.
I'd say Brighton is pretty similar too in that respect. Can even head over to Margate if you're feeling a tad more hipster. Both will probably bemissing a little off their charm in the winter without warm weather but still got stuff going on and places to visit.
You've also got Oxford/Cambridge if you're after a 'classical' English city - lots of beautiful old buildings and nice eateries.
Alternatively, if you're looking for a break from cities Lake District, Cotswolds, Cornwall (etc.) would all provide some great landscapes and nice village-y pubs.
But yeah, depends what you're looking to spend your time doing.