The details of this row, now rumbling on for over a month, are familiar – but the pressure is escalating.

Angela Rayner bought a council house in Vicarage Road, Stockport, under right-to-buy for £79,000 in 2007 and sold it in March 2015, shortly before she became an MP, for £127,500.

In 2010, she married Mark Rayner and they had two children.

If she moved into his home, a mile away in Lowndes Lane – which neighbours say she did, and her own tweets have described it as her “home” – then Vicarage Road was no longer her main residence and she should have paid tax on her £48,500 gain.

She insists she was not liable for it and has taken tax advice which backs that up. Sir Keir Starmer on Monday morning said his team – but not him – had seen that advice, which has not been made public.

Let’s be clear, if she did owe tax, the amount she was liable for is not in the big leagues. With estate agent fees and other exemptions, tax experts estimate it could be just £1,500.

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As Ray McCann, past president of the Chartered Institute of Taxation told me today, it could be nothing if, for example, she improved her home by putting in a new kitchen. We don’t have the full details.

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Ms Rayner has said she lived in her own home the whole time, and that she had an older child from a previous relationship.

“Every family is different, but it worked for us”, she said. She called the claims, which surfaced in a biography of her by former Tory donor Lord Ashcroft called The Red Queen, “a stream of smears from the usual suspects”.

Tax adviser Mr McCann said: “I don’t think there’s any credible case to be made that she’s deliberately evaded tax. I don’t see that as likely.

“Worst case scenario is that she didn’t realise it. She wasn’t Angela Rayner, deputy leader of the Labour Party, she was a care worker. These rules are very complicated.”

He points out that mistakes can be remedied with HMRC within four years so it’s now out of time – although she could choose to pay money back if found to owe anything.

There is a separate question of whether she breached electoral law by being registered at Vicarage Road if she didn’t live there – which Greater Manchester Police is looking at for a second time after Conservatives raised concerns.

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The Mail newspapers, which serialised the Lord Ashcroft book, are pursuing the story, publishing a letter today from the Conservative chairman Richard Holden with a list of unanswered questions.

But is any of the mud sticking?

Labour sources see this as another “Beergate” – the story about Sir Keir’s alleged lockdown-busting trip to Durham, for which he was eventually cleared by Durham Police.

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But the endless run of stories about the trip had, according to pollsters, an impact on trust in politicians across the spectrum.

Scarlett Maguire of JL Partners said: “That story didn’t cut through, until it did. Although he was cleared, we still had people bringing it up in focus groups years later.”

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Ms Rayner has often been Labour’s attack dog – calling on Rishi Sunak to sack Nadhim Zahawi over his tax affairs (in the millions of pounds) and asked questions about the prime minister’s billionaire wife’s non-domiciled status.

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Labour colleagues say this is no comparison, given the difference in scale, and she should not have to publish details of her personal affairs.

But this has now become a question of trust for a Labour leader who promised to clean up politics.

The Conservatives will be keeping the pressure on, and Labour will have to decide whether to bow to that pressure to reveal more details.

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