File, Preferences, Spell Check - select English (United Kingdom) in the primary dictionary and click “Set as Default”. This set is for Notes rich text.
File, Preferences, IBM Lotus Symphony, Language Settings, Languages - select “English UK”,
and add English UK dictionary and choose default dictionary in File > Preferences > IBM Lotus Symphony > Language Settings > Spell Check
File, Preferences, Sametime, Spell Checking - set “English (United Kingdom)” for Dictionary language. And restart Notes Client.
Please try these and come back if it does not work.
Thanks for the tips. I eventually reinstalled my Notes client completely, and got rid of my old bookmark and desktop files. I have had to repopulate my workspace but it has fixed the spell-check problem.