Fascinating detail, and worth a read especially alongside the Edward Snowden revelations, which came out after this book yet this book goes into much the same detail.

This book appears to make the point that services like GCHQ had their highlight in the 1950s and 1960s, and are now increasingly irrelevant: finding it hard to deal with the sheer amount of electronic communication. Unlike Snowden, the author here is sympathetic to the eavesdropping services, rather than critical: and is an interesting counterpoint.

With interesting tales of derring-do in history, this is certainly worth a read.