Keir Starmer was having fun. It’s been a long time since it was much fun to sit on the Labour front bench. It certainly wasn’t under Jeremy Corbyn, when party spokespeople had to choose a variety of carefully neutral expressions to maintain as their leader pondered aloud whether Vladimir Putin was really so bad. In the year since Corbyn disappeared, most of the government’s problems have related to Covid, a subject that is hardly a source of delight for anyone. But on Wednesday afternoon, there can have been few more enjoyable places to sit in Britain than the opposition front bench.

The subject was David Cameron and his employer, Greensill Capital. As we would be reminded more than once in the coming hours, Cameron said in 2010 that the next big scandal would be lobbying. What we didn’t realise at the time was that this was less a warning and more a manifesto commitment.

Starmer, like Boris Johnson opposite him, was wearing the regulation black tie and suit. But if his garb was funereal, his manner was anything but. He bounced out of his seat, pen in hand, smile on his face. He was in his happy place, prosecuting someone who was bang to rights.

“Does the Prime Minister believe that the current lobbying rules are fit for purpose?” he began.

Johnson played a defensive stroke. “I share the widespread concern about some of the stuff we are reading at the moment,” he said. There was going to be an investigation, and if the Labour leader had any information, he should share it with the inquiry.

But the prime minister is not by nature a safety-first batsman. Theresa May adored Geoff Boycott, and copied his dogged caution. Johnson sees himself as Ian Botham, or Ben Stokes, bashing the ball around the ground. When Starmer pressed on Greensill and Cameron, Johnson charged down the pitch, determined to slog the ball into the stands. “This is a government and a party that have been consistently tough on lobbying,” he said. It was Labour, he said, that wanted to repeal the Lobbying Act. Answer him that!

Starmer couldn’t have been more delighted. “He talks of the Lobbying Act,” he said, laughter in his voice. “Who was it who introduced that legislation? David Cameron.” Johnson looked troubled, the expression of a man who finds the ball has gone right past his bat and worryingly close to off stump. Starmer was still going, pointing out that the legislation Johnson was praising had allowed Cameron to act in a way that even Cameron now says shouldn’t have happened. He had another question: was the prime minister aware of any other government links with Greensill?

Starmer was in his element. “I have not heard a defence that ridiculous since my last days in the Crown Court,” he laughed.

Johnson was spooked now, back in his crease and just trying to see out the over. Did Starmer know something he didn’t? If he did, he replied, Labour should tell the inquiry. This is not the stance of a man confident of his own position. He tried another little stab at the ball: what about Labour ministers who had become lobbyists, like Lord Mandelson?

Starmer was in his element. “I have not heard a defence that ridiculous since my last days in the Crown Court,” he laughed. “It is called the shoplifters’ defence: ‘everyone else is nicking stuff, so why can’t I?’” He paused. “It never worked.”

For months, Johnson has labelled Starmer as an “Islington lawyer”, delivered in a tone of voice that suggests the legal profession is beneath contempt, unlike, say, Daily Telegraph columnists. The Labour leader is now leaning into the attack. “I remind the Prime Minister that I not only prosecuted shoplifters; I prosecuted MPs over the MPs’ expenses scandal, so I stand on my record.”

Starmer wanted to know why the Conservatives wouldn’t support a public inquiry by MPs. Imagine: hours of questioning of Cameron, Rishi Sunak, Matt Hancock and who knows who else, their text messages and WhatsApps published, their diaries dissected, their pub landlords being forced to explain how they’d won contracts to build fighter jets. Much better to have a quick investigation in private by a chap you can rely on.

We learned a bit more about the chap in question, Nigel Boardman, from Rachel Reeves, as she opened the subsequent debate on having a parliamentary inquiry. Reeves too was having the time of her life, landing punch after punch on the government. On Cameron’s semi-apology over Greensill, she was damning: “He’s sorry he got caught, and he’s sorry his shares are now worthless.”

And of Boardman, she was sceptical. “Some may suspect that the son of a former Conservative cabinet minister might be unlikely to make waves,” she observed. “Mr Boardman was appointed to a prestigious position at the British Museum by…” she paused, as though she had forgotten the next line, and looked around the chamber. “Oh! By David Cameron.” It was a bravura performance. At the end of the debate, Anneliese Dodds joined in too, highlighting Sunak’s disappearance from public view since the Greensill scandal broke. “At one point he tweeted proudly,” she said, “with the hashtag #AskRishi. We’d love to ask Rishi, but we’d have to find him first.”

For all the delight on the Labour front bench, it was a backbencher who secured the most interesting answer from the prime minister. Ruth Cadbury asked the last time he’d had contact with Cameron.

Johnson rose slowly. “Um,” he began. “The honest truth: I cannot remember the last time I spoke to Dave.”

Oh, the humanity. Oh, the pathos. It was as though Falstaff had decided he couldn’t be seen with Prince Hal. “I know thee not, old chum. Fall to thy prayers. How ill desert trips become a former prime minister.”

Poor David Cameron, cut off for impropriety by Boris Johnson, a man who is not so much a stranger to personal integrity as its sworn enemy. One could almost feel sorry for him.

Almost, but not quite.