Parliament’s standards watchdog has opened an investigation into the prime minister over possible failure to declare an interest.

The probe by the standards commissioner, Daniel Greenberg, was launched on 13 April and cited paragraph 6 of the MPs code of conduct, which governs how MPs should behave.

The code states that “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”.

A Downing Street source said the investigation relates to the shares his wife Akshata Murthy holds in a childcare agency that could benefit from a policy announced in the budget.

A spokesperson for Number 10 said: “We are happy to assist the Commissioner to clarify how this has been transparently declared as a ministerial interest.”

Sunak’s wife at centre of the investigation – politics latest

Mr Sunak faced accusations of a possible conflict of interest after he failed to mention Ms Murthy’s links to Koru Kids when he was questioned by MPs over why the financial announcement favoured private firms.

The i newspaper revealed that Companies House lists her as a shareholder in the organisation as recently as 6 March.

In a letter to parliament’s liaison committee, which quizzed the PM last month, Mr Sunak said: “I note that there has been some media coverage relating to the minority stake my wife has in relation to the company Koru Kids.

“I was being asked questions by the committee in my capacity as prime minister.

“I would like to clarify for the parliamentary record that this interest has rightly been declared to the Cabinet Office.”

He added: “The latest list of ministerial interests will be published shortly by the the independent adviser Sir Laurie Magnus.

“This regime ensures that steps are taken to avoid or mitigate any potential conflict of interest, and that the interests of ministers’ spouses or partners are not something that would influence their actions either as ministers or as members of parliament.”

The Liberal Democrats said last month that Ms Murthy’s shareholding raised “serious questions” and called on Sir Laurie to investigate.

And Labour’s deputy leader, Angela Rayner, said the PM “must explain why he failed to come clean” and provide a “proper explanation” of any steps he took to avoid any conflict of interest.

The prime minister is just the latest MP to investigated by the commissioner.

Last week investigations were opened into three MPs, including former health secretary Matt Hancock.

Scott Benton – who was recently caught in an undercover sting operation showing a willingness to lobby on behalf of the gambling industry – is also facing a probe, as is Henry Smith, the Conservative MP for Crawley.

Mr Benton, the MP for Blackpool South, is under investigation over the use of his parliamentary email address, while Mr Smith is also being investigated – for his use of parliamentary stationery provided by the public purse.

Meanwhile, Mr Hancock – who currently sits as an independent MP in the Commons following his appearance on I’m a Celebrity…Get Me Out of Here! – has been accused of lobbying parliament’s standards commissioner “in a manner calculated or intended to influence his consideration of whether a breach of the code of conduct has occurred”.

Mr Greenberg was appointed as the new independent standards commissioner last year and took over from his predecessor, Kathryn Stone, in January.