As I have been re-reading La Belle Sauvage, I have noticed some interesting things.
The first is the spangled ring, which Malcolm saw while reading. This was never fully explained and probably links to the secret commonwealth.
Hannah Relf leant Malcolm a book called The Silk Road. This book goes into detail about trade routes in The Levant. When discussing it, Malcolm says that this is the place he would most want to visit. Hannah says that maybe one day he will. Indeed, the setting for The Secret Commonwealth (which Malcolm appears in) is The Levant.