Everyone knew something bad must have happened before the Chancellor made his statement, though no one knew how bad it was. But gradually, as members of the Cabinet filed in, we realised it must be very serious. It’s normal for one or two Cabinet ministers to be there for moral support but never more than four or five. Yesterday, however, nine members of the Cabinet were there.

Then the Prime Minister himself entered, a picture of gravity, his new bright teeth tucked away behind grimly set lips.

“Oooohhhh!” screamed the Tories, already on pantomime form.

Alistair Darling, always quiet, was more subdued than ever (and that means close to comatose). He told us, with Poirot levels of detail, how two discs with “personal data relating to child benefit” had got lost in the post. As a tale it sounded as chaotic and incompetent as a Laurel and Hardy chase. The Tories gave him a scream soundtrack.

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BACKGROUND

• Police step in as other CDs have gone astray

• Moment’s blunder puts half the country at risk

• Data watchdog seeks dawn-raid powers

• New data law 'urgently needed'

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Hundreds of words, delivered in deadpan, had passed Mr Darling’s lips when he said: “The missing information contains details of all child benefit recipients: records for 25 million individuals.” At the words “25 million” there was a collective intake of breath. There were no screams. This was too serious.

And it got worse. “The records include the recipient and their children’s names, addresses and dates of birth. It includes child benefit numbers, national insurance numbers and, where relevant, bank or building society account details.”

The Chamber was shocked. The words “How could this happen?” hovered above MPs, as clear as if they had been skywritten. For this was that rarest of things: a disaster that affects MPs directly. Because among the details on those discs will be Mr Darling’s and Mr Brown’s, David Cameron’s and George Osborne’s.

Mr Darling then began a grovel of such spectacular proportions that I lost track of his expressions of regret. “We must make sure that this does not happen again, that we learn from this huge, massive, unforgivable mistake,” he said. Huge. Massive. Unforgivable. These are foreign words on the tongue of a government with a cast-iron rule of not admitting failure if at all possible. The Prime Minister’s face hardly moved throughout. His arms and legs were crossed. This is his pretzel posture, the political equivalent of the brace position for airline passengers.

Mr Osborne was scathing. “Let us be clear about the scale of this catastrophic mistake,” he said, words slicing the air in an almost violent manner. He went through the nightmarish detail of the Laurel and Hardy tale once again and Labour MPs were squirming. They hated this. Mr Osborne noted that ID cards must go and Labour hated that even more. They sat, fuming, muted only by the sheer size of this error.

Mr Osborne cast himself as the outraged Victorian papa, morally superior and utterly unforgiving. He looked at the huddle that was Mr Brown and noted that the Prime Minister had talked of wanting a vision. George sneered: “Never mind the lack of vision – just get a grip and deliver a basic level of competence.”

A pattern emerged. Grovel and abuse. Vince Cable is the acting leader of the Lib Dems and, boy, is he acting. There is no subject on which he is not an expert. “Home Office ministers have resigned on matters of honour. Treasury ministers declined to do so. Where does the buck stop in this Government?”

Mr Darling looked utterly miserable, like a dog who had just been whupped. What a week. First Northern Rock. Now this. His grovelling skills, if nothing else, are being honed.

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