Its basically "Basic Instinct" meets "Double Indemnity"...
... with a touch of Dahl's earlier works like "Kill Me Again" and "Red Rock West" (his best film in my opinion) and even "The Crying Game" on the side.
Very good film, yes, but also quite similar to those other aforementioned works. Right down to the theme of femme fatale being the main anti-heroine and the guy who thinks about himself and turns to dark sides and also even does something wrong himself in the process too.