The British parliament's Commissioner for Standards opened an investigation into Prime Minister Rishi Sunak earlier this month, according to a list of open inquiries posted on its website on Monday.

The list said the matter under investigation was a "declaration of interest". The inquiry began on April 13.

A spokesperson for Rishi Sunak said the investigation was linked to his wife's shareholding in a childcare firm.

The Liberal Democrats, an opposition party, had called for an investigation after media reports said Akshata Murthy was a shareholder in a company which would benefit from a government policy on funding for childcare announced in the March budget.

"We are happy to assist the Commissioner to clarify how this has been transparently declared as a ministerial interest," Mr Sunak's spokesperson said.

The Commissioner is responsible for monitoring the operation of the House of Commons Code of Conduct and Registers, including investigating any alleged breaches. The commissioner's page on the parliament website did not provide further details on the possible breach.

Under the code of conduct all members of parliament are required to "to provide information about any financial interest which might reasonably be thought by others to influence a Member's actions, speeches or votes in Parliament, or actions taken in his or her capacity as a Member of Parliament."

If the investigation finds Mr Sunak has broken the code of conduct, the Commissioner can require him to acknowledge and apologise for the breach and set out steps to avoid any future errors.

In more serious cases, the matter can be referred to a committee which has the power to impose other sanctions if it wishes to. These include oral or written apologies, suspension of salary, suspension from the service of the House for a specified period, or expulsion, according to the parliament website.