Have a look here:
http://www.lulu.com/uk
Yes, they're an American company, but they have a marketing arm in the UK, and their books are distributed from the same UK base as a lot of small publishers, so they're quite legit.
Basically, you upload your book through the website and choose your publishing options. You don't have to make it available to the public if you don't want to and there's no minimum order.
I've dealt with them before. Business-wise, they're OK. The products are good quality, and are delivered on time. Other than a monthly, online newsletter, they won't bombard you with sales literature either. They also have an online, live chat support if you have any problems - I used this at one point and found them very helpful.
It's worth taking time to have a really good look around the website before you upload, though. There are things like typesetting, fonts and covers to consider before you 'go for it', and it's worth knowing what your options are here.