You can try this method if you have a basement that is low in temperature and high in humidity. Dig your plants out, and shake the dirt of of the roots. Tie some twine about the stems and hang the geraniums from the basement ceiling. Occasionally during the winter take the plants down and let the roots soak in a pot of water for several hours. Once soaked hang them back up.There is no light required for this method. Replant in the ground when season is appropriate for your area.
Another method is to take cuttings dip ends in rooting powder place in vermiculite or other starting material and you know the rest of this method.
This age old hanging method comes from a Mennonite Farm down the road from me. They sell some veggies fruit and flowers at a roadside stand which they grow on their farm. This is a method I learned in talking to the farmer from time to time though I have not had the chance to use it since my house is built on a concrete slab due to high water tables in the area.

If you have a room in the house which is unheated, you can overwinter them in there - cut down the top growth by about 2 thirds, remove to large pots or boxes, or leave in their current pots, whichever's easiest and stand on a wardrobe or whatever.
Otherwise you can try them in the coldframe, closed to keep the damp out, but if we have a severe winter, that may not be enough. If you're really desperate and have nowhere else, a shed or garage, especially if there's some daylight there, provided the temperature in them doesn't go below about -5 deg. C. Keep them dry, dust with sulphur powder before moving to their wintering positions. Also check periodically and remove any fallen leaves as soon as possible to discourage fungus.

Hello Bamboo. Do you mean you leave the roots in soil but keep dry. Funnily enough, I remember as a child having my dads geraniums on the top of my wardrobe, can smell them now, lol but that's all I can remember.

Thanks Eclectric for your excellent explanation, but sadly i've not got a cellar. I do have a cupboard under the stairs i could try some in, or on top of a wardrobe as Bamboo suggested. I might try in all different places and just hope one of them works.
Thanks very much for all the advice everyone :-)

Yes, I do mean leave the roots in the soil and keep them dry, Dawnsaunt - only works in unheated rooms though, in somewhere that's heated they will need a drop or two every month perhaps. You don't want them to grow, you just want to keep them alive, and fungal infection is the biggest enemy.

Many of the older houses have detached root cellars in my area; they, together with spring houses were the two must items to have in the days before electrification. If you do have some space available one can be built in the garden utilizing a 55 gallon drum. Type in" building a small root cellar" on your web engine and you will come across that idea and others.

There are some older houses with cellars here, Eclectic, but frankly, generally suffer from damp, so not a great place to overwinter pelargoniums. I guess large country houses probably have dry cellars though.

Thank you Bamboo, I'll do what you say.

Yes bamboo. In my locale there are quite a few farmers and locals who for religious reasons shun electrification, thus many of the old methods of agriculture, food perservation, and plant propagation are still in use to this day whereas in most other areas these methods are extinct. Their farms and gardens are beautiful and once I get a camera with a good telephoto lens I will post some pictures for they do not like to have their images on camera. To them, it is an unacceptable act of pride.

UK's such a damp old place, really - I know that cellars are pretty common in USA though.

Good news, i think at least 20 have survived the winter in my makeshift double glazed cold ground frame thingy i made lol

That's good Bill. Got mine re-potted today but not sure if they are OK or not, some ends of stems are a bit soggy :-/

This works for me, I dig them out, put them in a pot with fresh compost and put on a windowsill, I dont cut them back, make sure they dont dry out too much, remove any dead foliage and they double in size, in the spring I pot them into fresh compost and then plant them out.