Re: And this ladies and gentlemen...
https://www.autoexpress.co.uk/car-news/96260/uk-car-number-plates-explained-rules-history-and-what-they-mean
States that O isn't used, For example the letters ‘I’, ‘O’, ‘I’ and ‘Z’ are never seen on number plates
And they have that comment immediately under a photo of a car with plate "EK16 LLO".
They're wrong anyway, my first car had a Co. Down plate beginning FOI and had a digit 1 in the number, and the letter Z is common in NI plates as well.