The subject says it all.

http://www.steamlocomotive.com/lists/?country=UK

At the moment, it's mainly operational steam locomotives 12-inch gauge (300 mm) or higher that are not travelling or on temporary loan away from their home base. You can of course submit these additional locomotives, submit non-operational steam locomotives, or make corrections and updates to the existing entries if you like by notifying the webmaster.

Steamlocomotive.com now has data for all of North America, the UK, Ireland, Australia, and New Zealand.