David Cameron left office with a song in his heart. Britain’s 53rd prime minister had just finished his resignation statement outside 10 Downing Street in July 2016, and as he walked back toward the recognizable black door, his pocket microphone picked up the sound of him humming a little tune: “Do dooooo, doo-doo.” Some detected a touch of The West Wing, others thought it was Wagner, but it was more of an amiable Winnie-the-Pooh sort of tiddely-pom, a sound that indicated a man at ease with his decision.

As the door closed, Cameron was heard to say “Right …” absentmindedly. I wrote in the next day’s Times of London that he sounded “as if he were the Earl of Grantham just returned from rogering one of Downton Abbey’s maids and not sure of how else to pass the afternoon.”

Cameron has since spent the past five years not being sure. Few things are as ex as an ex–prime minister, and Cameron was only 49, the youngest to leave office since Archibald Primrose, in 1895. He was not ready to become Someone Who Was. He wanted to still be considered in the present tense. At first he did the usual things: a few directorships, some charity roles, signing on with a speakers’ agency. More recently, Cameron converted his company to unlimited status, removing the obligation to deliver annual accounts.

He bought himself a $32,000 shepherd’s hut in which to write his memoirs, for which he reportedly received an advance of $1.1 million, less than a fifth of what Tony Blair, his predecessor, had gotten for his. Perhaps that difference rankled, just as it may have irritated him to hear that Nick Clegg, his former deputy, was earning a reported $656,000 a year with Facebook (not counting options), or that George Osborne, his chancellor, was getting $900,000 for advising BlackRock, the enormous investment fund—and for working just one day a week.

David Cameron reportedly “wanted to assist” Lex Greensill’s plans to open a new office in Riyadh.

Enormous riches would, however, soon be dangled in front of Cameron. In August 2018, he took a role as adviser to Greensill Capital, a supply-chain-finance firm owned by Lex Greensill, an Australian businessman whom Cameron had brought into his circle when he was prime minister—providing Greensill with a No. 10 business card and e-mail address as part of his unofficial role. Cameron’s compensation came partly in share options said to be worth some $60 million, though that figure is unconfirmed.

It’s academic now. Greensill went bankrupt in March 2021, but only after Cameron had pulled every string he could lay his hands on to try to keep it afloat. It is this intense activity that now casts a cloud over his reputation. Back in 2010, when he was the opposition leader, Cameron described lobbying as “the next big scandal waiting to happen.” In the same speech, he promised to shine “the light of transparency” on the cozy and lucrative relationship between business and politics, or as he put it: “crony capitalism.”

Alas, he did not follow his own advice on leaving office. Earlier evidence of his lobbying dates from 2019, when he arranged a drink between Greensill and Matt Hancock, the health secretary, to discuss plans for a wage-advance system. He then accompanied Greensill to Saudi Arabia in January 2020 to meet Crown Prince Mohammed bin Salman and discuss a regional office. Cameron and Greensill were pictured together on that trip, sitting cross-legged and sipping tea in a tent under the night sky.

Cameron’s compensation came partly in share options said to be worth some $60 million.

As the pandemic spread rapidly in March 2020, Cameron’s lobbying became more heated. With concerns being raised about how global supply chains would be affected, he e-mailed officials at the Bank of England, asking them to meet Greensill, who wanted support for his lending operations. The next month, Cameron texted Rishi Sunak, the chancellor of the Exchequer, several times, as well as government officials, begging for Greensill to be included in a government loan program aimed at keeping businesses afloat.

Greensill’s company suggested that a facility of between $15 and $30 billion was needed. The released e-mail thread shows Cameron’s tone becoming increasingly pleading, telling the bank’s deputy governor that it is “incredibly frustrating” not to have been given “the green light.” Two months later, the Treasury rejected Greensill’s proposal.

Cameron insists he broke no rules but accepts that he should have gone through formal channels. Boris Johnson, who became prime minister in July 2019, has ordered an independent investigation, described by one senior Conservative M.P. in the Financial Times as “Boris … getting his vengeance on Dave,” while a former minister said Johnson “will love nothing more than throwing Dave under the bus.”

Once a top government adviser to Boris Johnson, Dominic Cummings now describes his former boss as “mad and totally unethical.”

The two have had a difficult relationship for 40 years, having known each other at Eton and Oxford, where they were members of the infamous Bullingdon drinking society. Both were elected to Parliament in 2001, but while Cameron became leader of the party after four years, Johnson walked away to serve two terms as mayor of London before returning as the standard-bearer for Britain’s withdrawal from the European Union. His victory in the 2016 Brexit referendum led to Cameron’s resignation.

Johnson now has his own problems, however, after a series of stories were leaked to newspapers criticizing his handling of the pandemic, including a claim that he promised to waive tax rules so that the inventor Sir James Dyson could supply ventilators to the health service, as well as leaks about the prime minister’s asking party donors to pay for the refurbishment of the Downing Street living quarters.

On April 22, three newspapers were briefed that Johnson believes the source of these leaks was Dominic Cummings, his gnomish, combative former chief adviser and the lead architect of the Brexit campaign, who had been exiled from Downing Street six months earlier.

Johnson “will love nothing more than throwing Dave under the bus.”

Cummings’s response was swift and brutal. In a lengthy post the next day, he denied leaking but said that the renovation proposal was “unethical, foolish [and] possibly illegal,” and that the prime minister and his office “fall so far below the standards of competence and integrity the country deserves.”

Cummings has agreed to appear before M.P.’s on May 26 and take questions for as long as they want. He is a man who bears a grudge and knows where the bodies are buried. Westminster-watchers are already preparing the popcorn. Last weekend, Conservative insiders were saying that the prime minister had been unwise to, as one put it, “poke the bear.”

So the 40-year rivalry rolls on. Having started the week under a cloud, Cameron may be amused by how quickly the spotlight has shifted away from him. It may even lead him to hum another happy tune.

Patrick Kidd is editor of the Diary column in The Times of London