Spare a thought for the beleaguered inmates of Number 10 and especially for Sir Gus O’Donnell, the country’s top civil servant. As Downing Street reels under the combined impact of the lost Gurkha vote, the “smeargate” scandal and prime minister Gordon Brown’s inept handling of the row over MPs’ expenses, I learn that Sir Gus finds himself facing an unusual dilemma. The problem is Damian “McPoison” McBride, forced to resign as one of Brown’s close aides after revelations that he was planning to put out false and damaging stories about leading Tories. Someone leaked Mr McB’s plans to Paul Staines, better known as the blogger Guido Fawkes. The question is: who talked?

Sir Gus, according to one well placed source, was musing on whether to hold a leak inquiry or not. (What is it about senior officials and leak inquiries? What will it take to make them realise that leak inquiries are nearly always damaging to everyone concerned – except the leaker, nearly always a cabinet minister?) On this occasion even Sir Gus decided it would not be worth the candle. Why? Because, it seems, he reckoned that Mr McB was loathed by so many people at Number 10 that the investigators would have had to interview at least 70 suspects – pretty much the entire staff. It would appear that the only person in Number 10 who liked Mr McB was Gordon Brown.