Amis's foray into speculative fiction examines an alternative history in which England remains Catholic, the Papacy retains its hegemony, and young Hubert Anvil's soprano voice is so exceptional that his elders and betters propose to preserve it by castration.  His best novel of the 70s depicting life under a religious totalitarian government with at the core an adventure story.  

Things mentioned:

Philip K Dick The Man in the High Castle (1962)
Len Deighton SS GB (1978)
Robert Harrris Fatherland (1992)

John Salisbury - Kinglsey Amis YouTube playlist 
Kingsley Amis on the Russell Harty Show (1975)
Audiobook The Alteration