Gordon Brown in many ways looks a new man these days. I have never seen him, as Prime Minister, look as confident as he did yesterday in the House. It must be said that David Cameron is also a new man, and not in a good way. Indeed, did I say man? Perhaps I should have said mouse.

The most revealing moment came at the end of Dave’s attack on Gordon. The Leader of the Opposition was railing on about the budget deficit which, he said, some claim could hit £64 billion. “Isn’t the £64 billion question this?” cried Dave. “Why, when business and families need more help, has he left the cupboard so bare?”

Mr Brown’s head dipped to one side but on his face, instead of the usual irritation and frustration, his lips twitched into a bemused half-smile. This was a new smile, almost playful, and, unlike his other smiles, it looked entirely real. If cats could smile, then this is the smile they would have when, having caught a mouse, they let it loose for the sheer fun of batting it about, their claws temporarily sheathed. Gordo ignored the £64 billion question (he deals only in trillions now). “Let me just say that the reason we can borrow at this time,” he said, his paw flicking at Dave, “is that our levels of national debt are so low!”

The Tories rumbled. The secret half-smile came out again. Gordo said that he had noticed that Dave, on the radio that morning, had not seemed to know if the policy to borrow was right or not. “It is!” cried Gordo, who then celebrated his own wonderfulness as only he can, by reading out a list of IMF net debt comparisons in which Britain looked in fabulous shape compared with France, Germany, Italy, the US and Japan. Dave looked at him balefully. Gordo teased him again: “I would have thought that after weeks of discussing these issues you would understand that you cannot solve this problem unless you get to the root cause of the problem!”

The Tories were shouting at him now: “You! You!” Gordon’s lips twitched again. As the roar continued, he repeated himself and the Tories again shouted: “You!” Gordon repeated it again. Our Prime Minister, previously unable to see a joke even in a Christmas cracker, was loving this absurd panto. Indeed, he was goading them on. Dave was looking daggers now.

The paw was back out. Gordon was teasing them all about how the Tories’ attempt at all-party support had lasted only a few days. “I have to tell him that everybody’s judgment is being tested here. When we took the decision on Northern Rock, they opposed it. When we took the decision on Bradford & Bingley, they opposed it. When we intervened to deal with speculation in the shares market, they opposed it.”

Dave was shouting now too: “Rubbish! Rubbish!” Gordo tried not to smirk. He had made the mouse squeak. I could almost see his whiskers twitch with great contentment. The Speaker interrupted the mini-uproar. “Order! Let the Prime Minister speak.”

But when he did, Gordo only teased Dave even more about why the Tories do not have a policy. He then embarked on a tribute to himself that was followed by a series of Labour MPs standing up to heap further extravagant praise upon him. Gordon lapped it up. This is his moment and he is enjoying himself as the cat that got the cream.

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