Ex-PM in retreat following book (5)
I believe the answer is:
blair
'ex-pm' is the definition.
I can't judge whether this defines the answer.
'retreat following book' is the wordplay.
'retreat' becomes 'lair' (both can mean a private hideout).
'following' means one lot of letters go next to another.
'book' becomes 'b' (abbreviation for book).
'lair' put after 'b' is 'BLAIR'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for blair that I've seen before include "He followed Smith as party leader" , "See 3" , "Is the politician a Libra?" , "George Orwell's actual family name" , "Former prime minister" .)