Or you could simply use a browser which incorporates its own spell checker, i.e. Firefox:
http://www.mozilla.com/en-US/firefox/
(By default, Firefox uses US English. Go the the 'Add Ons' link, and select 'Dictionaries' to switch to UK English).
Chris
(PS: I've got so used to seeing my answers automatically subjected to spell-checking that, until I saw your post, I'd forgotten that some poor souls don't have this facility. The vast majority of the 'regulars' in AB's Technology section use Firefox. Perhaps it's time to join us?)