Alternative history novelists are a pretty unimaginative bunch – the Second World War is I suppose such a compelling period of history, when tiny moments can be seen to have had, in hindsight, such momentous impact, that they rarely stray far from its grasp. The turning point in this version of German victory in WW2 is Chamberlain’s resignation in 1940, and Halifax’s acceptance of the premiership. Surrender on terms to Germany swiftly follows.

So far so pedestrian, but Sansom sets his novel 12 years on, in a downtrodden England when the resistance is gaining momentum, Hitler is ailing, and the never ending war between Greater Germany and the USSR is draining the life out of the Reich. This world is realised in a lot of detail with alternative histories laid out for the rest of the world, the British political establishment (including Oswald Mosley and Enoch Powell, foreign secretary, and of course, irresistibly, Churchill, leader of the resistance) and various other British institutions.

What follows is a highly conventional spy narrative, with several strands closely interwoven, never more than a day or two apart. The principal character, David Fitzgerald, a fairly anonymous civil servant finds himself involved in a spy ring. By coincidence Frank Muncaster, a depressive university friend of his, becomes aware of some highly secret information which must not fall into German hands. This is all hugely unconvincing – it is never explained why the USA would want to try to smuggle Muncaster out of the UK when they already have the knowledge he carries. When the secret is finally revealed it is all one big “meh”, and the novel fizzles out of a beach in Rottingdean, of all places. For much of the novel this implausibility doesn’t really matter – Sansom drives the plot along convincingly and doesn’t allow too much time for reflection. The period detail, clearly the result of a lot of research, gives the book the feel of a 1950s black and white movie.

This was an undemanding, very long, read, that was an interesting digression on the “what if” theme, with a reassuring “we win the war in the end anyway” conclusion which I would not be at all surprised to see televised sooner or later.