There are some that start with a 0 too. With those the 020 is always needed so there are used for numbers that are redirected from others such as 0845 and not normally manually dialled.
Seeing 0207 or 0208 annoys me too. It didn't help that when the numbers starting 3 were introduced, it was all over the news as a new dialling code for London, confusing people even more
Not helped by news articles like https://www.standard.co.uk/news/0203-to-be-third-telephone-code-7233279.html
I seem to remember another article which implied that ALL London numbers were changing AGAIN...