British Conservative Party chair Nadhim Zahawi was fired from the government by Prime Minister Rishi Sunak on Sunday after a probe into the former's tax affairs found a serious breach of the ministerial code.

Sunak had ordered an independent adviser to investigate questions over the tax affairs of Zahawi, who was briefly finance minister during a period of political turmoil in Britain last year.

Zahawi has said Britain's tax authorities ruled he had been "careless" with his declarations but hadn't deliberately made an error in paying less tax.

"Following the completion of the Independent Adviser’s investigation – the findings of which he has shared with us both – it is clear that there has been a serious breach of the Ministerial Code," Sunak said in a letter to Zahawi.

"As a result, I have informed you of my decision to remove you from your position in His Majesty’s Government."

The independent adviser Laurie Magnus found that Zahawi had been misleading when he said that reports last July over his tax affairs were "clearly smears."

Zahawi did not correct the record until last week when he said he had reached a settlement with the authorities.

"I consider that this delay in correcting an untrue public statement is inconsistent with the requirement for openness," Magnus said in a letter to Sunak.

He added that Zahawi had shown "insufficient regard" for the requirement "to be honest, open and an exemplary leader through his own behavior."

"Mr. Zahawi's conduct as a Minister has fallen below the high standards that, as Prime Minister, you rightly expect from those who serve in your government," he said.