The wonderful rejuvenating effects of “Tory sleaze” were today demonstrated in the most striking way by Sir Keir Starmer.

It is hard to remember a time when he has looked so perky at the Dispatch Box. He turned pink with pleasure, just the right colour for his politics, as he contemplated “the sleaze that’s at the heart of this Conservative Government”.

He evidently believed it was back to the good old days of the 1990s, when Labour under a bright new leader, a former barrister resident in North London, destroyed the clapped out John Major Government with its “Back to Basics” campaign and its infinite supply of minor but horribly embarrassing scandals.

“There’s a revolving door, indeed an open door,” Sir Keir claimed, between Boris Johnson’s Government and paid lobbyists.

David Cameron and Lex Greensill had been photographed “camping out in the Saudi desert having a cup of tea”.

Surely, some of us thought, a cup of coffee? But Boris Johnson wisely declined to contest the point.

Did the Prime Minister look downcast? Was he abashed? Did he turn pale under this onslaught?

No sign of that. After all, he has never in his life launched a Back to Basics campaign, and never will. He’s a live and let live sort of a guy, quite different, though he did not mention it, to Cameron, who when moral issues came up liked to strike a note of Anglican asperity.

Johnson suggested it was a bit rich to hear this stuff from the Leader of the Opposition, who was being advised by Lord Mandelson of Global Counsel Limited.

“Perhaps in the interests of full transparency,” Johnson suggested, “Lord Mandelson could be encouraged to disclose his other clients!”

“I haven’t heard a defence that ridiculous since my last days in the Crown Court!” Sir Keir chortled, turning yet pinker with pleasure. “It’s called the shoplifter’s defence: ‘Everyone else is nicking stuff so why can’t I?'”

The time, he insisted, had come “to overhaul the whole broken system”, and to hold, as Labour is urging, a full, transparent, independent inquiry: “To quote David Cameron, his old school friend, sunlight is the best disinfectant.”

Again, Johnson declined to correct an obvious inaccuracy. He and Cameron were on friendly terms, but were not friends. Their mentalities could scarcely be less compatible.

The Prime Minister nevertheless picked up the reference to school. He said that to have an investigation by a parliamentary committee, as urged by Labour, would be useless: “His solution is yet again to have politicians marking their own homework.”

Not, perhaps, the most flattering thing to say about the House of Commons, but quite likely true.

Ruth Cadbury (Lab, Brentford and Isleworth) asked Johnson when he last spoke to Cameron.

Johnson, airly: “The honest truth, I cannot remember when I last spoke to Dave, but if she wants to know if I’ve had any contact with him about any of the matters that have been in the press, the answer is no.”

Hywel Williams (Plaid Cymru, Arfon) wondered whether the PM agreed “that on important matters of public policy politicians must not lie”.

Johnson: “We all concur with the basic principle that he’s just enunciated.”