LONDON — From the second Prime Minister Rishi Sunak of Britain took occupancy of 10 Downing Street final October, he has been haunted by his predecessors: Boris Johnson, defenestrated after serial scandals, and Liz Truss, deposed after an ill-fated foray into trickle-down economics.

On Thursday afternoon, Mr. Sunak’s authorities faces a deadline to show over Mr. Johnson’s Covid-era textual content messages, diaries and notebooks to a committee investigating Britain’s dealing with of the pandemic. It is the newest chapter in what looks like a endless reckoning with Mr. Johnson’s messy tenure.

Yet for all of the headlines that Mr. Johnson’s misadventures have commanded in latest weeks — together with new allegations of flouting Covid lockdown guidelines — it’s the ghost of Mr. Sunak’s short-lived predecessor, Ms. Truss, that economists say ought to hold him up at night time.

Yields on British authorities bonds soared final week to just about the degrees that introduced down Ms. Truss after solely 45 days in workplace. While the reason for this spike may be very totally different from that underneath Ms. Truss — fears that inflation is deeply rooted in Britain somewhat than horror on the earlier authorities’s proposed tax cuts — the political value to Mr. Sunak may very well be virtually as grave, with an election looming within the subsequent 18 months.

Mr. Johnson’s story “is, to some extent, surface froth,” mentioned Tim Bale, a professor of politics at Queen Mary, University of London. “That isn’t to say that the Boris Johnson soap opera can’t damage Sunak,” he added. “But what drives voters is the more profound question of the economy.”

On that challenge, the market gyrations are a nasty omen. They sign that buyers imagine the Bank of England must hike rates of interest quite a bit additional to tamp down Britain’s stubbornly excessive inflation, which may tip the struggling economic system into recession. Fear of price hikes led to the cancellation of almost 800 mortgage offers, which harm people who find themselves attempting to purchase properties.

It additionally raises the danger that Mr. Sunak will fall in need of one in all his cardinal pledges as prime minister: to chop inflation in half by the top of 2023. Although the inflation price dipped under double digits final week, to eight.7 p.c, costs for meals remained unexpectedly excessive. Britain has now diverged from Germany, France and Spain, the place inflation is far decrease and is dropping quicker than the economists predicted.

“The notion of ‘sick man of Europe’ has struck again, and when that happens, it’s hard to shake it off,” mentioned Jonathan Powell, a former chief of workers to Prime Minister Tony Blair. “Sunak keeps being dragged back to the bad old times.”

In the case of Mr. Johnson, these dangerous outdated occasions embody the lockdown-breaking events held in Downing Street in 2020 and 2021, which resulted in police fines for each the prime minister and Mr. Sunak, then serving as chancellor of the Exchequer.

The newest flap started when the chairwoman of the Covid-19 Inquiry, Baroness Heather Hallett, requested the Cabinet Office at hand over all communications between Mr. Johnson and fellow ministers through the pandemic, together with WhatsApp messages, which have turn out to be a well-liked method for officers to remain in contact.

The Cabinet Office has to this point balked, arguing that it has a accountability to guard the privateness of ministers. It has refused at hand over what it calls “unambiguously irrelevant” materials. Ms. Hallett has pressed for unredacted variations of messages, contending that it’s the job of the inquiry committee to determine what info is related to its investigation of the federal government’s Covid coverage.

The Cabinet Office, analysts mentioned, is cautious of setting a precedent and anxious that the disclosure of private exchanges may embarrass senior officers, together with Mr. Sunak. More than 100,000 WhatsApp messages belonging to a former well being secretary, Matt Hancock, have been leaked to the Daily Telegraph in February, providing an unflattering glimpse into how senior officers talked concerning the pandemic.

In one textual content alternate, Mr. Hancock mocked “Eat Out to Help Out,” a program designed to lure individuals again to eating places, which was sponsored by Mr. Sunak. He referred to it as “eat out to help the virus get about.”

In one other, the federal government’s high civil servant, Simon Case, warned that Mr. Johnson was a “nationally distrusted” determine who mustn’t announce new social-distancing guidelines throughout a bleak part of the pandemic in 2020.

“In a sense, this is our first WhatsApp inquiry,” mentioned Jill Rutter, a former civil servant who’s now a senior analysis fellow on the U.Ok. in a Changing Europe, a suppose tank in London. “One of the problems is that officials do things in deeply casual ways on WhatsApp. They mix the personal with policy and politics.”

On Wednesday night, Mr. Johnson mentioned he had submitted a trove of textual content messages and different materials to the Cabinet Office, and he challenged officers at hand it over to the inquiry in unredacted kind.

That additional complicates the dilemma for the federal government, since officers had earlier mentioned they now not had entry to the fabric. It places Mr. Sunak in a clumsy spot, because the authorities may face a authorized problem if it refuses to conform, which seems seemingly.

Mr. Johnson has had a cold rapport with Mr. Sunak since final July, when Mr. Sunak’s resignation as chancellor set the stage for Mr. Johnson’s downfall.

The former prime minister expressed anger final week when the Cabinet Office referred contemporary claims to the police that Mr. Johnson had violated lockdown laws by inviting mates to his nation residence, Chequers.

“Nobody has very high expectations of Boris Johnson,” Ms. Rutter mentioned, “but Rishi Sunak may be worried about what might be disclosed.”

Given that the inquiry could not conclude till 2027, the prime minister doesn’t must worry the knowledge popping out till after the following election, which he should name by January 2025. But he is not going to have that luxurious with the economic system, which is casting an extended shadow over the way forward for his Conservative Party.

Mr. Sunak, a former Goldman Sachs funding banker, succeeded in calming the markets after he changed Ms. Truss and reversed her insurance policies. Her budget-busting tax cuts have been considered as so reckless that monetary analysts took to calling Britain’s elevated bond yields a “moron risk premium.”

“In contrast to the moron risk premium, which was driven by crashing the institutions and generally appearing incompetent, this is quite different,” mentioned Jonathan Portes, a professor of economics at King’s College London. “This is pretty clearly down to the recent inflation numbers.”

Where some analysts say Mr. Sunak erred was in setting a tough goal for reducing inflation, particularly because the Bank of England, not the federal government, possesses the levers to do this. What as soon as appeared like a straightforward win now seems to be contact and go.

“The market thinks the U.K. has a persistent inflation problem, relative to other advanced economies,” Professor Portes mentioned.