Retain 'e' where required for pronunciation in words such as:
(It can be difficult to hear the 'e' in the pronunciation of these words. So, as always, if in doubt, check the first spelling given in the online Oxford Learner's Dictionary)
When adding '-able,' drop a final silent '-e' at the end of the stem
Keep the 'e' if dropping it would change the pronunciation of the preceding consonant
The only common exceptions are sizeable and saleable (although sizable and salable are US spellings—so, expect to observe this spelling when reading a variety of texts).
The '-yse' form is the only correct spelling for words such as paralyse and analyse (even in American and Oxford English)
Follow the convention of doubling a final -l after a short vowel on adding -ing or -ed to verbs (sole exception: parallel, paralleled) and adding -er to make nouns from verbs:
Other consonants double only if the last syllable of the root verb is stressed or carries a strong secondary stress:
but (exceptions):
Exception: a few verbs in -p (e.g. handicapped, kidnapped, worshipped, but not developed). Use -ct- not -x- in connection, reflection, etc. But note complexion and flexion.
European Commission English Style Guide - A handbook for authors and translators in the European Commission Eighth edition: January 2016. Last updated: July 2023 "[PDF File]" Retrieved from https://commission.europa.eu/system/files/2023-07/styleguide_english_dgt_en.pdf
University of Oxford Style Guide. "[PDF File]" Retrieved from https://www.ox.ac.uk/public-affairs/style-guide?wssl=