The confident, urbane demeanour of Whitehall’s top civil servants has been disturbed.

One of them may soon be outed as the source of an astonishingly indiscreet newspaper story in which he attacked Gordon Brown’s “bunker mentality” and even extended the criticism to his own boss, Sir Gus O’Donnell, the Cabinet Secretary.

The report, which appeared in the Financial Times last week, unusually gave several clues to the identity of the person who told the journalist Sue Cameron of his misgivings about the way Mr Brown is running the country.

Since then, the story has been used as the basis for a plethora of articles across the press describing Mr Brown’s allegedly strained relationship with leading civil servants and ministers. Sir Gus is known to be “spitting tacks”.

Now, to the horror of Whitehall and the journalists who report it, the name of the mandarin may emerge with disastrous consequences for himself and possibly for that most hallowed of institutions, the off-the-record lunch.

A request has been submitted to the Cabinet Office under the Freedom of Information (FoI) Act asking which permanent secretaries have had meetings with Ms Cameron in recent days. She surprisingly revealed in her article that the official was a man, a knight, that he enjoyed his wine and that they ate in an Italian restaurant.

Several permanent secretaries have been eliminated from the mole hunt on the basis of information supplied in the article, and The Times understands that, within Whitehall, the search has already been narrowed down to three.

If the FoI request is successful it will have serious implications for the working relationship between civil servants and politicians and the journalists who take them to lunch and dinner.

The career prospects of the source are not good. “It’s nonsense to think of Brown as a principled man who wants a new constitutional settlement,” the source said, as he ate his veal chop.

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