Well-placed moles have played a central role in the history of warfare and diplomacy since at least the time of Ancient China and Ancient Greece. Equally, however, it should be clear that the obsession with more recent moles is distorting our view of the role played by intelligence more generally. The significance of the breaking of the German Enigma code at Bletchley Park was that it was a collective enterprise of applied intelligence, rather than a scoop from a sweat-beaded agent playing a double game in an SS uniform.
And there is much to be said for the "open source" theory, which is that the West and the Soviets knew most about each other from published materials and the application of that most useful tool of analysis, common sense.
If there are serious lessons from the stories of the spying great-granny and the Scotland Yard detective, John Symonds, they are that we should put aside as much of the glamour and dramatic stereotype as we are able, and approach these issues dispassionately.
The immediate practical question is, should Mrs Norwood or any of the other "traitors" be prosecuted? Many would argue that Mrs Norwood's taste in clothes is more objectionable than the sale of secrets long ago. In principle, of course, a crime is a crime. It would be wrong for her to escape simply because of the passage of time, or because she is old, looks harmless or has great-grandchildren. General Pinochet is 83, and has a large family. And it is also right to pursue those guilty of crimes against humanity in the Second World War. But there has to be some proportion between the seriousness of the crime and the length of time since it was committed.
On that basis, the cases of Mrs Norwood and Mr Symonds are marginal. It all depends how much damage their crimes caused, either to national security or to the lives of other British citizens. Past traitors tend to have been dealt with in secret, for fear of making the security services look foolish. That approach will no longer do. It is vitally important that the Home Secretary, when he weighs the damage against the passage of time, does so as openly as possible.