I read the first hundred pages of [SS-GB] with mounting enthusiasm. The action was plausible, the characterisation firm and the surveying intelligence adult and well-informed….

Deighton is good on insignia, badges of rank, uniforms, military protocol. He is especially good on German inter-service rivalries and has clearly researched them exhaustively. If the Germans had come to London, then doubtless the Gestapo, the regular Wehrmacht, the SD, the Abwehr, the SS, the Geheime Feldpolizei and all the rest would have jostled and quarrelled in something like this way.

But, of course, they didn't come to London. And from about Page 100, the subversive thought kept surfacing: what is the point of this kind of historical 'might have been'? It has, of course, been used in the past to make some significant historical or metaphysical statement. But if there was any such intention here I failed to spot it….

Much of...