I'm not in the UK, but have many disabled friends who are and am in some UK-based disability message boards or other groups. My advice is based on what I know of how UK stuff works and I do know some things are changing (so may not be as available now) due to all the cuts Cameron has pushed through.
If you have a social worker, you might want to ask for a social services evaluation by an OT. If you don't have a social worker, you still might do well to call up and see about getting one and asking for an evaluation. That would not only look at the stairlift, but the OT might be able to suggest other equipment or adaptions for the house that would make your life easier! Depending on income and savings, you may be able to get some things provided through your local Council or grants to fund putting things in.
Also, there are Centres for Independent Living around the UK. If you can find your local one, they may have info about companies that other people in your area have had luck with when it comes to stairlifts.
If you want, I can PM you the site for another message board that may have more info. The majority of users are in the UK and most are very well informed about what's out there in terms of equipment and advice/help. (Most people on that board originally met on a BBC message board that got shut down and someone opened up a different message board to replace the BBC one.)