Keir Starmer often strident in opposition struggles to maintain probity in government | Rachel Reeves

There’s a theory in British politics, often attributed to Tony Blair, that you need to be careful when throwing a boomerang at the opposition because once you’re in power it may come back and hit you in the face.

As opposition leader, Keir Starmer has become adept at dealing blows to the Conservatives. He called on Boris Johnson to resign for breaking the rules, particularly over the Partygate scandal. “You can’t be a vigilante and a law breaker, and it’s time to pack your bags,” he said.

He took a huge political gamble and said he would resign if found guilty after Durham police launched an investigation into whether he breached lockdown rules by drinking beer and curry at a campaign event. Luckily for him, it wasn’t like that.

At the time, Lisa Nandy described him as “Mr Rules”, drawing on the contrast between Starmer’s seemingly high ethical standards and Johnson’s carelessness, perhaps not entirely helpful for the Labor leader who voters thought was already a bit on edge.

Since coming to power, the boomerang seems to have swung towards the prime minister with a vengeance. Maintaining this level of integrity, not only for himself but also for his cabinet, was always going to be an impossible task, especially in the flawed world of politics.

But few predicted that Starmer would be the first to undermine his own position, failing to see that accepting free glasses, clothes and Taylor Swift tickets could break even the slightest belief that his government would be different.

Since then, scandals have proliferated, although they vary in degree of severity. Louise Haigh was forced to resign as transport secretary last November after it was revealed she was found guilty of fraud over a lost work phone in 2014.

Tulip Siddiq resigned as Treasury secretary in January after Bangladesh’s ousted prime minister acknowledged the government was hurt by his close ties to his aunt, who is now accused of corruption.

The departure of Starmer’s deputy Angela Rayner in September after breaching the ministerial code for underpaying stamp duty on her £800,000 seaside flat was the most serious blow yet.

But Starmer was always clear that there would be no special treatment. “People will only believe we’re changing politics if I fire someone on the spot. If a minister – any minister – seriously breaks the rules, they’ll be expelled. It doesn’t matter who it is, they’ll be sacked,” he told biographer Tom Baldwin before the election.

When it emerged on Wednesday that Rachel Reeves, who is second only to the prime minister in terms of seniority, might be in a difficult position, it sent a collective shudder at the top of the government. If the chancellor goes, the entire Starmer project could collapse.

Having apparently learned the lesson of the Rayner row, Downing Street acted decisively to announce that the chancellor had admitted “mistakenly” breaking housing rules by renting out his south London home without the £945 special license required by the local council.

Not only that, the Prime Minister had already spoken to Reeves, consulted ethics adviser Laurie Magnus and decided within hours of the Daily Mail story being published that further investigation into the matter was “not necessary”.

By early Thursday morning, government officials were confident that while Reeves had made a mistake, he had an excuse: The rental agency had not informed him that his home was a designated area requiring a permit. He quickly corrected the error by submitting an application.

But Kemi Badenoch, thought to be behind the story by Tory researchers, was determined to get the scalp. “This whole thing stinks. The Prime Minister needs to stop trying to cover this up, launch a thorough investigation, and if Reeves broke the law, get emboldened and fire him,” he posted.

Downing Street initially failed to draw a line under Magnus’ story, refusing to say whether it had seen any evidence to support the claim that Reeves had made an “inadvertent” mistake, or whether he had breached the ministerial code or broken the law by breaching Southwark council rules.

Fortunately, Reeves had the receipts. Her husband pulled up emails from the rental agency where they rented their home. Just before publication, the rep released a statement saying he was apologizing to the couple for an “oversight” that meant they were unable to obtain a licence.

Chancellor seems clear, but there are still questions about why his story changed overnight: From not knowing a license was required to the agency telling them it would apply to them.

Additionally, the law clearly states that it is the property owner, not the rental agency, who is legally responsible for the application. It is also unclear how the couple failed to realize that almost £1,000 was missing from their bank account.

While the offending was relatively minor compared to the multitude of offenses committed during previous Tory administrations, Reeves’ failure to comply with the standards regime highlights the difficulties of Starmer’s stance on ethics.

The ambition to restore the broken public trust in the political classes, slowly eroding after years of scandals, is understandable. But when the boomerang returns, the pitfalls of taking the moral high ground are clear: People are fallible.