British finance minister Rishi Sunak adhered to rules on conflicts of interest and the ministerial code regarding his and his family's financial affairs and his holding a U.S. "green card", an independent adviser to the government said.

"I advise that the requirements of the Ministerial Code have been adhered to by the Chancellor, and that he has been assiduous in meeting his obligations and in engaging with this investigation," the adviser said in a statement on Wednesday.

"In reaching these judgements, I am confined to the question of conflicts of interest and the requirements of the Ministerial Code. My role does not touch on any wider question of the merits of such interests or arrangements," he said.

Sunak faced criticism this month when his wife - a daughter of an Indian billionaire - confirmed that she had non-domiciled tax status in Britain, something opposition lawmakers said was incompatible with Sunak's plans to raise taxes on workers.

He was also criticised for holding a U.S. "green card" - an immigration status intended for permanent U.S. residents - after he became finance minister in 2020.

Until recently, Sunak was seen as a strong candidate to eventually become prime minister. But the recent spotlight on him, combined with criticism of his decision not to offer fresh support for households hit by surging inflation, have seen his popularity fall in opinion polls.

Earlier this month, Sunak asked for the independent advisor to consider whether he had broken any rules.