This is the compendious, brilliant, chest-crushing, 1,000-page authorised history of MI5. It’s authorised to the extent that Andrew was allowed access to all 400,000 MI5 files. There then began a debate with MI5 about what he was allowed to write. So it is a partial history; it cannot be the full history. Yet it contains astonishing stories, really remarkable insights into how MI5 was run.