You have many options, but in January, the weather can have a huge impact. You will laugh, but here, two inches of snow grinds the country to a halt! Snow is less likely if you stick to the coast and lower altitudes. The main problem is the short daylight hours - c 8am to 4 pm. You are going to get a wide range of options, which probably won't make deciding any easier. Americans are going to suggest the usual London - Stonehenge - Bath - Cotswolds - Oxford - York etc loop all by train, but if you really want rural communities, cover less ground. The British are each going to suggest their local area!
Your options are to stick fairly close to Brighton, which post 1 covers or you could travel anywhere in the country - it depends what you want to see. A sensible loop would be Brighton - Lewes - Rye - Hastings - Battle - Dover (only the castle, the town is awful!) - Sandwich - Canterbury - Whitstable - Faversham. Plus Leeds Castle, Hever Castle, Penshurst Place, walk on the Downs and museums etc.
If you want to go a bit further, I would suggest Suffolk and Norfolk - coast, pretty villages and Norwich which is worth a visit. The more touristy option is the New Forest and Portsmouth (again, avoid the awful city centre, but good for naval history), but as this is second home/tourist territory, it will be quiet in January.
At that time of year, due to weather uncertainties, I would avoid visiting the Scottish Highlands, Peak District, Lake District or Snowdon, as there is a higher risk that you would have to cancel. Many of the National Trust properties will be closed for the winter but most of the independently owned properties will be open, if history is your thing.
Accommodation will not be booked up at that time of year so you can be flexible. Trip Advisor is useful, as is SAwdays website if you want nice, rural B&Bs. If you want rural communities, you really need a car to get about.
The trouble is that there are too any choices!
