Police are investigating allegations that Angela Rayner may have broken electoral law over information she gave about her living situation a decade ago.
It comes after Tory MP James Daly informed Greater Manchester Police (GMP) of claims made by neighbours that contradicted the Labour deputy leader’s statement that her property, separate from her husband’s, was her main residence.
GMP previously said it would not be investigating the allegations.
But the force has now “reassessed” information about the case and launched a probe following a complaint from Mr Daly, an MP in the region and the deputy chairman of the Conservative Party.
Politics latest: Angela Rayner ‘welcomes chance to set out facts’
A spokesperson for GMP said: “We’re investigating whether any offences have been committed.
“This follows a reassessment of the information provided to us by Mr Daly.”
Labour leader Sir Keir Starmer said the investigation “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 the Ashton-under-Lyne MP “welcomes the chance to set out the facts with the police”.
Ms Rayner has faced scrutiny over whether she paid the right amount of tax on the 2015 sale of her council house in Stockport, because of confusion over whether it was her principal residence.
The Labour frontbencher has rejected the allegation and denied any wrongdoing.
Sir Keir previously said the Conservatives were “chasing a smear” by raising questions about the deputy leader.
Mr Rayner bought a council house in Vicarage Road, Stockport, under right-to-buy rules 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, 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 had taken tax advice which backs that up.
Sir Keir on Monday morning said his team – but not him – had seen the tax advice, which has not been made public.
Tax experts have said that, while Ms Rayner may not owe anything, if she did the amount could be in the region of £1,500.
Ms Rayner has said 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 described the claims, which surfaced in a biography of her by former Tory donor Lord Ashcroft called The Red Queen, as “a stream of smears from the usual suspects”.
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Senior Labour figures leapt to Ms Rayner’s defence following the police statement.
London Mayor Sadiq Khan said he was fully confident that his “best friend” will be cleared.
Shadow climate minister Ed Milliband said Ms Rayner, who left school at 16 while pregnant with no qualifications, was “inspiring” and “exactly the kind of person we need in politics”.
“We are absolutely 100% behind Angela”, he added.
However, 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.