Angela Rayner is being investigated by police over allegations she may have broken electoral law.
The official police investigation was launched weeks after the row over her former living arrangements and tax affairs first erupted.
So what exactly is the deputy Labour leader accused of doing?
Here’s what you need to know.
What are the accusations?
The row centres on what house was Ms Rayner’s primary address ten years ago.
Ms Rayner said it was an ex-council house she used to own on Vicarage Road in Stockport, which she bought in 2007.
But she faces claims she lived primarily at her then husband’s address in Lowndes Lane, just over a mile away.
The pair married in 2010 and have two children together.
The claims she lived mainly at her ex-husband’s house matter because she was registered to vote at the Vicarage Road address.
Under electoral rules, voters must register at their permanent home address, and there are penalties for providing false information when registering to vote.
Then there is the issue of whether she paid the right amount of tax when she sold her house.
She sold the Vicarage Road house in 2015 for £127,500, having bought it at a 25% discount through the “right-to-buy” scheme for £79,000 in 2007.
If it was her primary address, as she has claimed, she would not have had to pay capital gains tax on the £48,500 profit.
But if she had moved to Lowndes Lane, she would have had to pay up.
Tax experts have said if Ms Rayner did owe tax, the amount could be in the region of £1,500.
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How did the accusations come out – and what have police said?
The claims first surfaced in February in Lord Ashcroft’s unauthorised biography, Red Queen, serialised in The Mail On Sunday.
The biography also includes claims that when Ms Rayner re-registered the births of two sons she shares with Mark Rayner in 2010, she gave her husband’s address.
Initially, Greater Manchester Police said there was no evidence of an offence being committed.
But on 12 April, the force said it had launched an investigation after “reassessing” information about the case.
It came after Tory MP James Daly informed police of claims made by neighbours that allegedly contradicted Ms Rayner’s statement that her property was her main residence.
In early April, The Mail On Sunday also claimed to have seen dozens of social media posts from Ms Rayner between 2010 and 2015, which it said showed her now ex’s address was her main property.
In response to those claims, a Labour Party spokesperson said: “Angela and her husband mutually decided to maintain their existing residences to reflect their family’s circumstances and they shared childcare responsibilities.
“Angela has always made clear she also spent time at her husband’s property when they had children and got married. She was perfectly entitled to do so.”
What has Angela Rayner said?
Ms Rayner has insisted she has done nothing wrong and said she received “expert tax advice” to confirm this.
However she has refused to publish the advice she received – unless her Tory critics do the same.
She has maintained she lived in her own home the whole time, and that the property was where she had raised her son from a previous relationship.
“Every family is different, but it worked for us”, she said. She called the claims in Lord Ashcroft’s biography “a stream of smears from the usual suspects”.
After the story first broke, Ms Rayner told journalists there was “never a question of deceitfulness” or “conspiracy” with regards to her living arrangements, as she outlined her “difficult” family situation at the time.
“I’ve talked about my upbringing and the difficulties and challenges – getting that house so that I could provide for my son was huge. That was so important to me – I weren’t just giving it up.”
After police launched their investigation, Ms Rayner said she will “do the right thing and step down” if she is found to have committed a crime.
“I am completely confident I’ve followed the rules at all times,” she said in a statement.
“I have always said that integrity and accountability are important in politics. That’s why it’s important that this is urgently looked at, independently and without political interference.”
Read more:
Angela Rayner’s tax affairs – a smear or a real trust problem?
The investigation into Labour deputy leader hinges on one thing
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What about her stance on right-to-buy?
While it’s not a legal issue, Ms Rayner has also been accused of hypocrisy for using the right-to-buy scheme, which she has previously criticised for giving some tenants “loads and loads of discount”.
The right-to-buy scheme was brought in by Margaret Thatcher and allows council or housing association tenants to buy their properties at a big discount, while authorities can only keep a third of the receipts from each sale to build a replacement home.
In 2012, David Cameron increased the discounts offered by the right-to-buy scheme after they were reduced by Tony Blair’s Labour government in 1997.
Ms Rayner has promised to review the high discounts introduced in 2012, as well as a review to stop newly-built social homes from being sold off.
She insisted she was not “ashamed” to have bought her council house at a discounted rate through the scheme.
In a post on X after the first Mail On Sunday article was shared, Ms Rayner said buying her home was a “proud moment for me”.
“I worked hard, saved and bought it by the book,” she said.
“I’m not ashamed – but I am angry that the Tories have since put the dream of a secure home out of reach for so many others.”
Ms Rayner has said Labour believes those who live in a council house “should have the opportunity to own their own home”.
“But the problem with the right-to-buy was never ordinary people’s dreams of owning their own home – it was that council housing stock was sold off and then not replaced,” she said.
What has the Labour Party said?
Following news of the police investigation, Labour leader Sir Keir Starmer said it “will allow a line to be drawn in relation to this matter” and added he was “fully confident that Angela Rayner has not broken the rules”.
He also said: “She will co-operate with the investigation, as you would expect, and it is really a matter for the police.”
A party spokesperson added that Ms Rayner “welcomes the chance to set out the facts with the police”.
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Sir Keir previously said the Conservatives were “chasing a smear” by raising the questions about the deputy leader.
He said his team had seen the legal advice provided to Ms Rayner about her tax affairs.
Shadow foreign secretary David Lammy told Sky News he was confident Ms Rayner had done “nothing wrong” and had “played by the rules”.
He said the allegations were being spread as part of the “political season” and to distract from “Tory chaos”.
What have the Conservatives said?
Defence Secretary Grant Shapps accused her of “double standards”, and said she had “spent her political career calling people out for exactly the thing that she seems to be doing now”.
“It’s important that it’s looked into properly and I welcome the idea that the police are doing that,” he added.
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What other scandals has the Labour Party faced recently?
This is not the first scandal to have rocked the Labour Party in recent months.
Labour’s Rochdale by-election candidate Azhar Ali was engulfed in an antisemitism row during his campaign for the seat – which the party had initially expected to win.
The party withdrew its support for Mr Ali after he claimed Israel allowed the Hamas atrocity of 7 October to happen in order to give it the “green light” to invade Gaza and made further comments blaming “people in the media from certain Jewish quarters” for fuelling criticism of a pro-Palestinian Labour MP.
Parliamentary candidate Graham Jones was also suspended from the party over “unacceptable” comments about Israel.