The quote from the article was > The terrible truth that began to dawn in the 1980s was that MI5 - whose job it was to catch spies that threatened Britain - ha

The quote from the article was > The terrible truth that began to dawn in the 1980s was that MI5 - whose job it was to catch spies that threatened Britain - had never by its own devices caught a spy in its entire history. Which is correct. MI5 only had that information thanks to the work of MI6, not by its own devices.