Westminster Cathedral is a popular haunt of Catholics in and around London. It is a good place to meet (several places to eat nearby) and, being near Victoria Station, it is easy to make a detour there when visiting London.
There are two bookshops accessible from the Piazza in front of the Cathedral: St Pauls Bookshop and the CTS. St Pauls occupies a cavernous area below ground and has plenty of space to walk around the bookshelves and browse.
The CTS has far less shelf space and is quite poky. It is the kind of shop where you have to negotiate past people and there is little elbow room.
Despite the different sizes of the shops, I find that I can spend an hour browsing St Pauls and come out empty-handed whereas in the CTS I have to get out after five or ten minutes in order not to have bought too many books to carry home comfortably on the train. I rarely seem to visit there without coming out with at least three books and making mental notes to look up others on Amazon later.
I don't mean to be unkind to St Pauls - I don't normally buy books in shops nowadays in any case. But somehow the constantly updated stock at the CTS proves irresistible - they have the kind of books that I buy just in case they prove unobtainable on the internet.