Have a look at page 7 here: https://www.birthrights.org.uk/wp-content/uploads/2019/10/Caesarean-Section-Guideline-4.pdf At the moment you're planning a category 4 (planned) c-section, if you were to go into labour before that planned date it would be moved up to a category 3 or 2 depending on exactly what was happening - only the category 1 is a true "emergency" c-section. As Sam commented, they wouldn't book you in before 39 weeks without a good clinical reason, as baby has higher chances of complications like breathing difficulties as their lungs are not mature. I've heard from others that you get your elective c-section date at your 34w appointment so not too much longer to wait :)
My first was booked for week 39 but she came early at week 38 so it was on paper an “emergency” cat 3 but it was not. I walked myself in, still had a really chilled experience and nothing felt emergency about it. Baby 2 I got ICP and there was a pathology lab strike so my original section of week 38 (to avoid early labour again) turned into week 37.
They book you in for 39 weeks and if you go into labour beforehand it’s classed as an “emergency” c section but they’ll just bring what you’ve already planned forward. It’s not like a dramatic emergency. They won’t book you in earlier unless you have a complication.