Mr Rusbridger, a former businessman and MI6 agent, is an indefatigable writer to national newspaper editors. His letters range over a wide variety of subjects, frequently offering his views on sloppy habits of modern intelligence men, though never on the subject of the IRA.
He has a no-nonsense style which some find irritating. Nevertheless, he was alarmed to receive in the post on 23 November a letter addressed to 'James Rusbridger, Chairman, Cornish IRA Supporters League, Lanivet, Nr Bodmin.'
The letter, signed 'R F Hudson & family & friends' and addressed only 'London W13 2XL', said: 'Dear Rusbridger, We note that you are still banging on about our country's treatment of Irish murderers . . . It is only people like you - detribalised shits - who rush to give comfort and, therefore, support to the Irish murderers.'
Mr Rusbridger's amusement ('I thought it funny at first') turned to dismay when he realised that several people, including the postman, might have noted the words on the envelope.
Who knew what lunatics, or Ulster Protestant loyalists, might be living near Bodmin?
'So, having failed to find Mr Hudson's name in the London phone book,' he said, 'I wrote to the police, politely asking them to trace him and call upon him, suggesting that such letter-writing, aside from being untrue, could lead to a breach of the peace.' He enclosed a copy of Mr Hudson's envelope.
An administrative officer of the Metropolitan Police then sent Mr Rusbridger a postcard dated 30 November, which promised that 'the matter is receiving attention'.
But Mr Rusbridger's dismay increased when he examined the front of the postcard, marked 'On Her Majesty's Service Commissioner of Police' and overprinted with the words 'Crime Stoppers'.
It was addressed to 'James Rusbridger, (Chairman) Cornish IRA Supporters League, Lanivet, Nr Bodmin.'