Those worried about the health of British politics have diagnosed a new disease at Westminster.

Chris Patten, a grandee from the Conservative establishment, spotted what he called “Long Boris” last summer.

Weeks after Boris Johnson announced his resignation as prime minister, Lord Patten, a former party chairman and former BBC chairman, lamented the persistent “corrupting and debilitating impact of Johnson’s premiership on British politics and government.”

As with ‘SARS-Covid-19’ there was some debate as to how the condition should be named in general conversation.

Eventually, “Long Johnson” was settled on rather than the more familiar “Long Boris”.

The commentator Paul Waugh listed some of the symptoms of Long Johnson he saw in the bloodstream of the Conservative party: “A debilitating condition that led it to lose its sense of taste, decency and direction.”

Long Johnson hit fever pitch with the Conservative party’s short-lived collective decision to select Johnson’s preferred candidate, Liz Truss, as the next prime minister. That quickly burnt itself out.

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On taking office Rishi Sunak tried to shake off Long Johnson by promising that his government would be one of “integrity, professionalism and accountability” at all times. It is not proving so easy for the new prime minister to escape unwanted legacies from his predecessor-but-one.

Questions of probity over two men who were promoted by Johnson, Nadhim Zahawi and Richard Sharp, have combined to create the biggest political crisis of Sunak’s short premiership.

According to Raphael Behr, political columnist on The Guardian, the “Zahawi episode is a symptom of Long Johnson, the chronic, recurrent, debilitation of government by a pathogen that still circulates in the ruling party long after the original infection has been treated”.

The embarrassments Sunak is grappling with are debilitating hangovers from the Johnson era, so is the fumbling way the prime minister is dealing with them.

Nadhim Zahawi had the reputation at Westminster of a comparatively competent and personable minister, one of those credited with the successful roll-out of the vaccine programme. But as often with politicians who become conspicuously wealthy there was much gossip about his finances.

His wealth was generated as a co-founder of the polling company YouGov before he became an MP.

Scrutiny of Zahawi’s finances sharpened when he became Chancellor of the Exchequer, the politician responsible for the nation’s finances and tax system. In seeking the truth, journalists received what they considered to be aggressive threats of libel from lawyers acting for Zahawi, designed to suppress allegations, some of which have been confirmed as accurate.

It is now known that while he was Chancellor, Zahawi quietly negotiated a tax settlement totalling some £5m, including a penalty of more than £1m, with Her Majesty’s Revenue and Customs (HMRC) for which he was the minister responsible.

Zahawi says his mistake was “careless but not deliberate”. Jim Harra, the head of HMRC, told MPs this week: “There are no penalties for innocent errors in your tax affairs.”

There is no pressing reason why Boris Johnson should have made Zahawi chancellor. Nor does the haste with which the appointment was made suggest that the prime minister or his officials, led by the Cabinet Secretary, had sufficient time for due diligence looking into his suitability for this most sensitive financial post. Yet their green light then effectively gave him a free pass to prominent ministerial ranks under both Truss and Sunak.

By late last year scrutiny by an honours committee elsewhere in Whitehall reportedly held up a proposed knighthood for Zahawi.

In the past, when serving prime ministers have announced their intention to resign, other ministers have stayed in post until the successor is chosen. He or she then assembles their own cabinet team. This has been so even when threatened ministerial resignations force out a prime minister, as happened to both Tony Blair and Boris Johnson.

Once he announced he was going, Johnson could have said that he was not accepting resignations and that all minsters would stay on in the interim. That is not the way Boris Johnson behaved. He used his dying powers of patronage to settle scores and to try to influence the outcome of the leadership election.

He fired Michael Gove and then he troubled the ailing Queen to appoint an entirely new temporary cabinet for the few weeks of the leadership contest. Johnson promoted Zahawi to the Treasury, thus crucially depriving Rishi Sunak of the status of high office during the leadership battle, while Truss luxuriated in the great office of state of foreign secretary.

Earlier, after Sunak emerged as the person most likely to replace Johnson, he became the subject of damaging leaks about his US Green Card and his wife’s non-dom status. The Metropolitan Police coincidentally tarnished the teetotal Sunak’s reputation, and blunted the impact on Johnson, by issuing them both with fixed penalty notices for breaking COVID regulations at the “ambushed with a cake” Johnson birthday party in the cabinet room.

Sunak experienced the hard way the phenomenon, now hitting Zahawi and Sharp, that friendship with Johnson often has adverse consequences.

Richard Sharp insists that he was appointed the chairman of the BBC on merit after a rigorous selection process. There is no reason to doubt his perspective. When I knew him at university, more than 40 years ago, he was an exceptionally decent and considerate person. He went on to build a highly successful career in finance alongside generous voluntary contributions to public service and charity.

Men with known political affiliations such as Michael Grade, Gavyn Davies and Marmaduke Hussey have been appointed to the BBC chair by other prime ministers. But Boris Johnson made the final decision over Sharp, after he and his allies had previously broken with precedent by conjuring up culture wars and pre-endorsing friends and allies such as Paul Dacre and Charles Moore for top posts in the media, normally viewed as apolitical – unsuccessfully it turned out.

Johnson used his patronage to appoint Peter Cruddas to the House of Lords, someone who had helped him out with his personal finances. Richard Sharp says he “simply connected” people, who then facilitated an undeclared personal £800,000 overdraft guarantee for the prime minister.

Richard Sharp and cabinet secretary Simon Case may genuinely have decided this was immaterial to Sharp’s BBC application but is that the way Boris Johnson sees things? Several enquiries into Sharp’s appointment are now under way. Johnson’s benefactor Sam Blyth is an old friend of Sharp.

The inquiries will doubtless ascertain whether Boris Johnson knew of this obliging distant cousin’s existence before Sharp introduced him to the cabinet secretary.

Long Johnson is also evident in the way the government is handling these potential scandals.

Quick resignations and moving on are things of the past. Following a pattern which became familiar during the Johnson era, Sunak has presided over, and sometimes joined in, denials that have turned out to be inaccurate, playing for time by calling for further inquiries after awkward facts are established.

Sir Keir Starmer had a two-pronged attack at PMQs: “We all know why the prime minister was reluctant to ask his party chair questions about family finances and tax avoidance, but his failure to sack him, when the whole country can see what is going on, shows how hopelessly weak he is.”

Sizeable minorities in parliament and perhaps even more in the Tory membership are not loyal to Sunak and hanker for a return of Johnson. This limits Sunak’s ability to lead firmly.

With his oblique reference to the great wealth of Sunak’s family, the leader of the opposition went further, implying that the prime minister is really just one of them – sharing similar values, or the absence of them, to Johnson and Zahawi and the same acquisitiveness.

Only urgent decisive action by Sunak can demonstrate that he has beaten the plague of Long Johnson.