Dominion, By CJ Sansom

The war was lost, now the battle begins

CJ Sansom is fascinated by the abuse of power, so it's not surprising that, hot on the heels of his splendid Shardlake series, comes a novel set in a post-war Britain dominated by Nazi ideology. Following the defeat at Dunkirk, the fascists have been in government for more than a decade, Churchill leads the Resistance, Jews are being deported and David Fitzgerald is a civil servant who has agreed to spy for – or against – his country.

There have been a number of other novels imagining this kind of alternate history – Robert Harris's Fatherland, Owen Sheers' Resistance, Len Deighton's SS-GB and, for children, Sally Gardner's Maggot Moon. All are outstanding in different ways but Sansom's Dominion is the most thoroughly imagined in all its ramifications.

Like Harris, Sansom has woven a thriller with the tale of a man's growth into moral courage, but he has done it with the compassion and richness that many literary writers should emulate. Every detail of this nightmare Britain rings true, from the way that morris dancing is televised as a cultural expression of nationalism to the absence of the name "Lyons" in Corner Houses. Cowardice and collaboration are everywhere. "We used to think the British people would never become Fascists … but … anybody can, given the right set of circumstances," David's wife, Sarah, says. The French will love this.

When Frank Muncaster, one of David's university friends, is sent to a lunatic asylum after learning a top scientific secret, all three are in mortal danger. David has kept his half-Jewish identity secret, and the Gestapo has put Gunther, a brilliant hunter of Jews, on his trail. Even though Hitler is declining with Parkinson's disease, the British government, led by Lord Beaverbrook, Oswald Mosley and Enoch Powell, will not stand up for British people.

As in Sansom's Winter in Madrid, the clash between compassion and political conviction is dramatised. David's looks and talent make him as freakish in his way as frail, disabled Frank, and the friendship between someone who can survive institutions and someone who cannot is one of the most affecting aspects of the novel. Sarah is a less satisfactory character: despite her well-drawn grief and jealousy, you never feel that she experiences the humiliating anxiety of intelligent women who are wholly dependent on their husbands.

Naturally, the weather is awful, and obliges with a choking, oily fog as our heroes battle against hideous odds to get to safety. But both as a historical novel and a thriller, Dominion is absorbing, mordant and written with a passionate persuasiveness. Furthermore, it is confident enough of itself to be published without a swastika on the cover. Bravo!

Amanda Craig's Hearts and Minds is published by Abacus