Fara Kids Charity Shops normally have maternity sections, and there are several across London.
Vinted - it’s amazing for maternity wear
I wud say if u buy new jus buy bigger a few essentials
Try vinted
Fara kids in Primrose hill
I told my SO this is just the kind of shop i want to open! (rather than ho back to my job) i hate online shopping and struggled so hard to find stuff
Try with vinted app