Desktop applications or online (browser)?
If desktop applications, see https://answers.microsoft.com/en-us/msoffice/forum/msoffice_word-mso_win10-msoversion_other/proofing-language-keeps-changing-solutions-how-can/c6483d0c-6fe3-41bf-8464-25535d3ec15b?tm=1579788821357.
Probably the biggest thing is to make sure that your Operating System language is also EN-UK.