This month marks exactly 300 years since the Whig statesman Robert Walpole officially became our first prime minister. Not only was the country squire and landowner the first politician to occupy 10 Downing Street, he has also served the longest time at the top: an unbroken 20-year reign dubbed the “Robinocracy”.

Most historians rate Walpole as one of our more successful prime ministers: he stabilised the nation’s finances, saw off Jacobite sedition, and kept the country out of foreign wars, proudly boasting: “There are 50,000 slain in Europe this year and not one Englishman.” But inevitably, there was a downside to Walpole: he was charged by his enemies with corruption.

Nobody can reasonably object to former premiers earning a crust on the international lecture circuit

In fact, considering the spectacular eighteenth-century standards of sleaze, Walpole was — to borrow a phrase coined by Tony Blair — “a pretty straight kind of guy”. True, he spent six months in the Tower of London accused by his political foes of all sorts of malpractice; but he was eventually cleared. True, too, that he built a magnificent mansion, Houghton Hall, in his native Norfolk — but he had legitimately made a fortune in the South Sea Bubble financial crash that ruined so many others (by buying shares when they were low and selling them when they were high). Nevertheless, Walpole was not above sailing close to the wind of propriety, cynically remarking: “Every man has his price.”

Neatly enough, as we celebrate this anniversary milestone in the evolution of parliamentary democracy, the financial affairs of two of Walpole’s fellow Old Etonian successors — David Cameron and Boris Johnson — are coming under scrutiny and criticism. All of which raises the interesting question of whether our political masters today are more — or less — honest, transparent and “straight” than they were in Walpole’s day.

By and large most former prime ministers have been stringent in their financial probity (though David Lloyd George dabbled in insider trading when he was chancellor in the 1910s and sold peerages and knighthoods to fund his political campaigns as prime minister in the early 1920s). Winston Churchill financed his expensive tastes with honest, Herculean hard work by churning out articles and books on a titanic scale. In recent years, however, such high standards have not only started to slip — they have slid south at a dizzying rate.

A Sunday Times investigation has revealed that, since his hasty departure from Downing Street in the wake of the 2016 Brexit referendum, Cameron worked as a lobbyist for the Australian-born financier Lex Greensill. The former PM is reported to have emailed chancellor Rishi Sunak pressing the claims of the company Greensill Capital for an emergency government loan to stave off its collapse. Cameron’s plea failed, and the company has now gone bust, putting thousands of jobs in the steel industry at risk.

Anyone who remembers the miasma of sleaze surrounding John Major’s regime may well feel an acute sense of déjà vu

It has since transpired that Mr Greensill worked inside Downing Street during Cameron’s premiership, and even had a business card calling him a “senior adviser (in the) Prime Minister’s Office”, complete with a Downing Street email address and phone number. As part of his lobbying activities Cameron was photographed glamping in the Saudi Arabian desert with Mohammad bin Salman, the Saudi Crown Prince, soon after the prince was reported to have ordered the gruesome murder and dismemberment of the dissident Jamal Khashoggi.

No one has suggested that Cameron’s lobbying was actually illegal, but the Labour Party has called for a Cabinet Office inquiry into the former PM’s dealings with Greensill and how the money man came to have a role at the heart of government. Cameron himself, who is said to have told friends at one stage that he stood to make up to £60 million from his shares in Greensill Capital, has gone to ground and made no comment on the affair in the days since the story broke.

Meanwhile, Boris Johnson is also in the spotlight on a number of financial fronts. There have been calls from Labour for further inquiries into the award of lucrative government contracts to companies with links to the Conservative Party during the Covid pandemic; into £126,000 paid to the company of Boris’s then-girlfriend Jennifer Arcuri during his time as mayor of London; and into the mystery donor who paid for the expensive refurbishment of the Downing Street flat occupied by Boris and his fiancée, Carrie Symonds.

Our politicians are now shoving their snouts into the trough with truly Walpolian eagerness

Again, no-one has yet suggested that anything illegal has been going on, and nobody can reasonably object to former premiers earning a crust on the international lecture circuit, but such unanswered questions are all too evocative of a government which has spent too long in power becoming contemptuous of the very rules that are supposed to keep politicians on the straight and narrow. Anyone who remembers the miasma of sleaze surrounding the dying days of John Major’s unlamented regime in the 1990s, and the 2009 MPs expenses scandal, may well feel an acute sense of déjà vu.

But Johnson and Cameron are still in the foothills of alleged financial gain compared to the Himalayan heights ascended by Major’s successor, Tony Blair. Since his departure from Downing Street in 2006, Blair has parlayed the contacts and influence he acquired during his lengthy tenure in No.10 into hard cash. His specialty seems to be advising tyrannical regimes in the Middle East and Caucasus, and he thinks nothing of being paid millions by oppressive dictators whose favoured methods of government are torture, murder, and repression.

There is an increasingly blurred line separating crooked illegal conduct with behaviour that is merely obscenely greedy, tasteless, and offensive to ordinary people’s ideas of decency. It appears that too many of our leading politicians are abandoning the moral standards that restrained such behaviour during the nineteenth and twentieth centuries, and are now shamelessly shoving their snouts into the trough with truly eighteenth-century Walpolian eagerness.