If you're talking about the annual geraniums you buy as bedding plants ( they're actually pelargoniums) then generally they won't survive a British winter outdoors. They will occasionally survive a very mild dryish winter

Most people just throw them out with the other summer bedding but if you pot them up in late autumn before the hard frosts you can over winter them in a frost free place and put them out again in late spring . They will do well on a window sill and flower all year around if you dead head them regularly.

I have some I keep indoors all year around as pot plants.

http://www.flickr.com/photos/31559373@N00/1018537129/

Native Geranium (cranesbill) do, but you may mean Pelargonium geranium instead - these are hardy down to -10 degrees, but they usually die outside over winter in the UK because of damp cold, when they succumb to fungal infections.

All the twenty perlargoniums I have in flower now in pots were overwintered. Some in a mini greenhouse. Others under fleece, sharing very large pots with other plants, mainly fuchsias. It can be done but you will have quite a few losses. Mainly due to stems going rotten. When they get potted on into much larger patio pots they usually grow away very rapidly.