There was a time when the top job in British intelligence was the head of MI5 or MI6. Today it is arguably the director of the Government Communications Headquarters, the secret listening centre in Cheltenham. The search is now on for a new GCHQ chief after the unexpected resignation yesterday of Robert Hannigan, for personal reasons.

In his two years in the post, Mr Hannigan has done a fine job in the face of changing circumstances. He has seen the threat from cyber‑warfare increase to the point where it is now the main challenge to British security.