The parliamentary commissioner for standards, Daniel Greenberg, ruled that Mr Sunak "confused" declaring his interests as a minister with registering his interests as an MP.

The inquiry by Mr Greenberg was launched in April after concerns were raised about the shares Akshata Murty held in the company Koru Kids, which was set to benefit from changes in the budget.

Mr Sunak did not mention his family's interest while being questioned by MPs at a committee hearing in March, but later declared it on the register of ministerial interests.

This list of interests for members of the government is separate from the registration of interests that all MPs have to maintain.

Mr Greenberg said: "In accordance with the code, Ms Murty's shareholding was a relevant interest that should have been declared during the Liaison Committee meeting on 28 March 2023."

He concluded that he was satisfied the prime minister had "confused" the two separate registration processes.

"I formed the view that the failure to declare arose out of this confusion and was accordingly inadvertent on the part of Mr Sunak," Mr Greenberg said.

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He added: "During a meeting with Mr Sunak on 30 June 2023 I acknowledged that he may not have been aware of Ms Murty's shareholding at the time of the Liaison Committee meeting, but he had a duty to correct the record.

"However, Mr Sunak was aware of the interest when he subsequently wrote to the chair of the Liaison Committee, Sir Bernard Jenkin MP, on 4 April 2023, and he failed to declare the interest at that stage or correct the record."

In a letter to the commissioner, Mr Sunak said: "Should this scenario arise again, I have acknowledged that I have a duty to write to the committee after my appearance to correct the record.

"I accept and once again apologise that my letter to the Liaison Committee on 4 April 2023 was not sufficiently expansive, as it confused the language of registration and declaration."

In the budget, Chancellor Jeremy Hunt announced a pilot of incentive payments of £600 for childminders joining the profession, a sum that doubles to £1,200 if they sign up through an agency.

Asked in the committee if he had any interest to declare when talking about how the policy was formed, Mr Sunak said: "No, all my disclosures are declared in the normal way."

Koru Kids was one of six childminder agencies in England listed on the government's website when the policy was announced. Ms Murty was listed as a shareholder in the most recently filed paperwork for the business on Companies House.

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The prime minister's press secretary said: "The commissioner's investigation into the prime minister's declaration of interest has been resolved by way of rectification.

"The prime minister takes seriously his responsibilities to register and declare all relevant interests."