Ha'penny

In 1949, eight years after the Peace with Honor was negotiated between Great Britain and Nazi Germany, England has completed its slide into fascist dictatorship. The last hopes of democracy seem extinguished. Then a bomb explodes in a London suburb. The brilliant, but compromised Inspector Carmichael of Scotland Yard is assigned the case. What he finds leads him to a conspiracy of peers and communists - of staunch King-and-country patriots and hardened IRA gunmen - to murder the Prime Minister and his ally, Adolf Hitler.

Synopsis from Open Library.