Rishi Sunak is under investigation by Parliament’s standards watchdog over a possible failure to declare an interest.
Parliamentary Commissioner for Standards Daniel Greenberg opened the inquiry under rules demanding MPs are “open and frank” in their declarations.
The complaint refers to the fact Sunak's wife, Akshata Murty, is a shareholder in childcare agency Koru Kids.
Labour MP Catherine McKinnell alluded to this when Sunak was giving evidence to the Commons liaison committee last month.
She implied that the firm would benefit from a decision in the budget and that Sunak should have declared his wife’s stake as a relevant interest.
Scottish Liberal Democrat MP and party chief whip Wendy Chamberlain then raised the issue with the Prime Minister's ethics adviser.
A source from Downing Street confirmed that the investigation relates to Murty's Koru Kids shares.
Downing Street said the Prime Minister will clarify how it was declared as a ministerial interest, rather than to the Commons.
An update to the parliamentary website on Monday showed the investigation, opened on Thursday, related to paragraph six of the MPs’ code of conduct.
“Members must always be open and frank in declaring any relevant interest in any proceeding of the House or its committees, and in any communications with ministers, members, public officials or public office holders,” the section reads.
A No 10 spokeswoman responded: “We are happy to assist the commissioner to clarify how this has been transparently declared as a ministerial interest.”
Chamberlain said: "Another day and another accusation of a Conservative Prime Minister bending the rules.
"This is on the same day that Rishi Sunak may have broken election rules for his government announcement today.
"After months of Conservative sleaze and scandal, the public just want a government which is focused on the country, rather than saving their own skin."
Labour deputy leader Angela Rayner said:
"This Government's failure to update the rules or publish a register of ministers' interests in nearly a year has left a transparency black hole which is enabling the Prime Minister and those he has appointed to dodge proper scrutiny of their affairs.
"If Rishi Sunak has got nothing to hide, he should commit to publishing the register before May's elections so the public can see for themselves.
"While this Prime Minister fails to deliver the integrity he promised and preserves the rotten standards regime he inherited as the Tories resist tighter rules, Labour has a plan to clean up politics with an Independent Ethics and Integrity Commission to restore standards in public life."
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