MI5 has been around for hundreds of years and faces down many enemies who routinely threaten the internal security of the United Kingdom. They are overworked, underpaid, and understaffed. Until recently, it was official government policy not to acknowledge they even existed, and the name of their Director-General was highly top-secret.

Despite their many triumphs during World War II, in particular the Double Cross system (where they turned captured German spies back against their German masters in a massive misinformation campaign), it was the Soviet KGB which almost brought MI5 down. As Chapman Pincher notes in his informative and engrossing book, Their Trade Is Treachery, KGB penetration of MI5 is suspected to have reached the very top – to the Director-General, Roger Hollis, himself (although that was never proven conclusively).

Everybody knows the big names – Kim Philby, Guy Burgess, Anthony Blunt, but the idea that the MI5 Director-General himself was passing information to the Russians – and betraying his own agents – is staggering to contemplate. When his own agents suspected him, he shut down all attempts to investigate him. He fired persistent colleagues who refused to give up, the Prime Ministers of the day were either kept in the dark or decided not to ask questions they didn’t want to know the answers to. In short, it was an institutional monumental fuck-up, the likes of which MI5 are still struggling to overcome over 40 years later.

Chapman Pincher was a newspaper journalist covering security stories. So he knew the players inside MI5 and MI6. He was fed information and his scoops helped bring down foreign spies and expose the failings of the agencies that were meant to be guarding British interests. Now he has brought all of that information together in this book – and it is a gripping, well written account.

My only complaint would be that it is extremely dated. It only goes up to the 1980’s, and since Pincher is long dead, there won’t be any sequels. But since the USSR died its own death at the end of the 1980’s, any sequel wouldn’t be that long anyway.

Saying that however, with Russia experiencing a resurgence and the FSB exercising its enormous clout again, this is a very timely book to read. You will be reminded that complacency leads to history repeating itself. Since we barely survived last time, a repeat would be disastrous.