Reuters
The Conservatives have called for an investigation into Deputy Prime Minister Angela Rayner's tax affairs.
The Daily Telegraph reported that she saved £40,000 in stamp duty when buying a flat in Hove, East Sussex, after telling tax authorities it was her main home.
Tory Party chairman Kevin Hollinrake has written to the prime minister's independent standards adviser asking him to investigate whether Rayner broke ministerial rules.
There is no suggestion she has broken any laws, but the Tories said this was "inappropriate tax avoidance for a minister subject to higher standards of conduct".
A spokesperson for Rayner said she paid "the relevant duty" owed "entirely properly".
It is understood Rayner's "primary residence" for council tax purposes remains her family home in her constituency of Ashton-under-Lyne, Tameside, but that following her divorce she ceased to own a stake in the property.
This meant she was able to avoid the higher rate of stamp duty that would have been applicable when buying the Hove flat if it had been classed as a second home, the Telegraph reported.
She paid £30,000 in stamp duty on the £800,000 flat in Hove, instead of £70,000, according to the paper.
Stamp duty is a tax paid when buying a property over a certain price in England and Northern Ireland.
In last autumn's Budget, the government increased the additional rate of stamp duty when buying a second home to 5%, on top of the standard rate.
As secretary of state for housing, communities and local government, Rayner is responsible for council tax and housing policy.
In his letter to Sir Laurie Magnus, the independent adviser on ministerial standards, Hollinrake said the arrangement amounted to "hypocritical tax avoidance, by a minister who supports higher taxes on family homes, high-value homes and second homes".
He also claimed it "collapses the house of cards that Tameside is her primary home".
As Deputy Prime Minister, Rayner also has a grace-and-favour flat in Admiralty House in central London.
Hollinrake argued this was "likely to be her primary home - where she spends the majority of her time as a minister".
He claimed Rayner had breached the Ministerial Code because "her tax affairs are not in good order".
Under the rules, ministers are asked to confirm their tax affairs are up to date and consistent with their overarching duty to comply with the law.
If Rayner was found to be in breach of the ministerial code, Hollinrake said Sir Laurie should consider sanctions, including "at the very least" stripping Rayner of her ministerial residence.
Separately, the Conservatives have written to Tameside Council, calling for Rayner to be struck off the electoral roll there, arguing it is not her "permanent" home.
They claimed she was currently registered at three addresses - in Ashton-under-Lyne, London and Hove.
Some people may be eligible to register at more than one address if they can be deemed resident at both, for example students who live at one address during term time and another during the holidays, according to the Electoral Commission.
However, the watchdog says owning a property or paying council tax are not on their own sufficient to establish someone is resident at an address.
Earlier, Health Minister Stephen Kinnock defended his colleague, telling LBC: "The deputy prime minister has made it absolutely clear she's done absolutely nothing wrong."
He added: "Everything that she's done is fully within the law."
A spokesperson for Rayner said: "The deputy prime minister paid the relevant duty owing on the purchase of the Hove property in line with relevant requirements and entirely properly, any suggestion otherwise is entirely without basis."