Ofsted: And Ofwat
OK: Use OK, not okay
On to: Is two separate words. Avoid ‘onto’ at all costs.
Online: One word, no hyphen
Only: Put it in front of the word it qualifies e.g. he waited only three weeks, not he only waited three weeks
Opposition: Is lower case, as is government
Open-heart surgery: Hyphen as open-plan room
Organisations, companies and councils are always a singular it, not a they, whether in copy or quotes.
Therefore, ‘The council has claimed it is in love with daffodils.’
not ‘The council have claimed they are in love with daffodils.’
Ouija: Note spelling
Over: Not a substitute for ‘more than’. When we are talking in terms of quantity, or numbers, it is always ‘more than’ or ‘fewer than’. See numbers
Overreact: No hyphen as overrule, override