No less an authority than John LeCarré has called this the best true spy story he’s ever read and it’s hard to argue. Oleg Gordievsky came from a devoted KGB household – both his father and his brother were KGB officers and he followed in their footsteps - but the construction of the Berlin Wall and the brutal suppression of the Prague Spring in 1968 turned his head against “the blind obedience and the cowardice of the Homo Sovieticus.”

A cultured man, his eyes are further opened when he gets a taste of western freedoms in Copenhagen and, after an extended courtship with MI6, he begins - for ideological reasons rather than material gain - sharing secrets with British intelligence. When he is posted to the shockingly paranoid London KGB offices matters intensify as the Brits conspire to have Gordievsky’s superiors removed from the country, allowing their man to climb ever higher, eventually becoming the head of station. There’s a strong argument to be made that Gordievsky was instrumental in pulling the world back from the brink of self-destruction and he provided vital insight into the madness at the heart of Soviet intelligence for western leaders like Reagan and Thatcher, who held him in very high esteem.

Thanks to meddling from a frustrated CIA officer, Aldrich Ames, Gordievsky is summoned back to Moscow and the story takes a different turn. The jig, it seems, is up. He’s drugged and interrogated but still manages to put MI6’s daring escape plan into action.

Ben Macintyre is an old hand at this kind of turn, as anyone who’s read his brilliant Agent Zigzag or Operation Mincemeat can attest, and he weaves together an utterly fascinating tale that leaves most fictional thrillers in the dust. You’ll be agape at the way things were.