Mr Osborne, David to Mr Brown's Goliath, came to the Dispatch Box and asked about the lamentable state of pensions: "I know the Chancellor doesn't do humility but does he accept any blame for what's gone wrong?"

The Chancellor responded by dwelling on some of the blunders which he says a Tory government would make about pensions. The Speaker rose and said: "He can't dwell on what is Conservative Party policy."

Mr Brown's lower lip chattered as he struggled to arrest the flood of words in which he was trying to drown Mr Osborne, who instead continued goading the Chancellor: "No one believes what he says about his own policies, let alone ours."

At this point Mr Brown lost his cool and threw his papers towards Mr Osborne. They landed beside the shadow chancellor's glass of water. This marked an amazing loss of self-control by Mr Brown. It was as if, like an adult who starts screaming at a naughty child, he had allowed himself to be dragged down to the level of his tormentor.

The interest in watching Mr Brown lies in wondering whether the red-hot passions that one can sense blazing within him will ever result in a volcanic eruption, or whether he can go on channelling all that fire into his relentless oratory.

Mr Osborne followed up by quoting an assessment which John Hutton, the pensions secretary, is supposed to have made of Mr Brown: "He'll make an effing awful Prime Minister."

The Speaker ordered Mr Osborne to withdraw, prompting the cheeky Tory to rise and say: "I of course unreservedly withdraw the quote from the Secretary of State for Pensions."