Becoming a doctor does not make you upper class in the UK. You can't really become upper class, at least in the traditional sense - certainly not through a job or money.

https://en.wikipedia.org/wiki/Social_class_in_the_United_Kin...

e.g. David Cameron, Eton educated prime-minister, described himself as middle class.

https://www.bbc.co.uk/news/magazine-25744526

Edit: You could argue that everyone is middle class these days - almost nobody self identifies as working class and there are so few real upper class people (I've never met one).

Edit2: Of course, you used to be able to buy entry into the upper class. But that doesn't happen anymore ;-)