If you like second hand book stores there’s a classic, if small, store that’s been around for ages in Hamstead (which if you’re visiting London for the first time is a great area to visit anyways), called Keith Fawkes.

Also check out the South Bank Book Market, again all second hand and antique books, located outdoors and underneath Waterloo bridge I believe, along the queens walk, which again is already a part of any trip to London for me with or without the books! Have a great trip!