A few years ago, I was present at a talk given by a retired intelligence chief of a friendly country. He mentioned, only partly humorously, how young recruits to his service were initiated into the mysteries of his craft by being taken on their first day of work to the old room where sealed envelopes had their flaps steamed opened, contents read, and then resealed, leaving the intended recipients none the wiser.

The craft of intelligence has developed from those discreet and seemingly gentlemanly days - it had to. The present era is one where nations face threats of a magnitude and sophistication that the spy chiefs of just a generation ago would have had some difficulty comprehending.