Unfortunately, Persephone Books had to move, but there is still a big selection of their books in Waterstones at Piccadilly Circus. This Waterstones is the biggest bookstore in Europe, it got 6 levels and a nice cafe. Foyles is also massive and right around the corner of Shaftesbury Avenue. For all kinds of LGBTQ+ books, I heartily recommend Gay’s the Word at Russel Square. They have a wonderful selection, great atmosphere, and they have a lot of signed books and special events with authors. Last but not least, for Fantasy, Sci-Fi and Comics, Forbidden Planet at Shaftesbury Avenue is another great store with lots of good deals and many signed books as well. Have fun in London!