The trouble with flowering plants in winter is, they don't flower much. Pansies are fine, but stop flowering if its really cold, and are really at their best by about March. You can use miniature cyclamen (available now) or ornamental cabbage, but these are only intended for autumn, so about 3 months. That leaves Christmas onwards... so the best solution is really a mix of pansies with good coloured foliage or berried plants. At this time of year, most garden centres stock small versions of Skimmia (with berries), Euonymus (variegated leaves), a range of small conifers with interesting foliage, and ivies, plain and variegated, to trail, for people to use in containers. Small versions of Heuchera, of which there is a very wide range of leaf colour, are also useful. As you live in the mild area of the country, polyanthus/primula/primrose are worth considering, because they probably flower earlier down there, along with early flowering bulbs such as snowdrops and aconite.

I would second the heuchera recommendation. Some of them have such beautiful leaves they're as good as flowers.

I bought three last year for my borders and they looked fabulous even through the 5-6 weeks of miserable cold weather we had in early spring

here they are

http://www.flickr.com/photos/31559373@N00/8054428058/

winter flowering heathers are also good for 2- 3 months flower. Some start in December others in January. they thrive in tubs

http://www.flickr.com/photos/31559373@N00/3380217786/in/photolist-69GuZ1-4J3b6n

Bamboo and Anchorman have good suggestions for you, I also would go with heucheras..... we have 3 [and I want lots more!] they are so pretty, with foliage like that you don't need flowers. They seem hardy too and need little care.Can you buy them at this time of year though? It could be a problem.

I saw several heuchera at a local garden centre a few days ago