The allegations, reported by the Sunday Times newspaper, have surfaced only days following criticism of Sunak for reappointing Suella Braverman as interior minister after she was fired by his predecessor for breaching email security rules.

The Sunday Times published text messages sent by Gavin Williamson, a minister in the cabinet office, to the former chief whip, or Conservative Party enforcer, Wendy Morton, in which he criticised her and used expletive-ridden language.

The newspaper said he was angry about not being invited to Queen Elizabeth's funeral and that Morton had made an official complaint to the governing party.

"These were said in the heat of the moment, expressing frustration. It was a difficult time for the party. I think he now accepts that he shouldn't have done it and he regrets doing so," Dowden told Sky News.

"He shouldn't have sent those messages ... But of course the prime minister continues to have confidence in Gavin Williamson."

A government source said Sunak was aware of a disagreement between Williamson and Morton.

Since being appointed as Britain's third prime minister in two months almost two weeks ago, Sunak has come under pressure over his government appointments, particularly Braverman's reappointment as interior minister.

She has been criticised by some lawmakers for inflaming tensions over immigration by saying Britain faces an "invasion" from people travelling in small boats crossing the English Channel.

"Rishi Sunak's pledge to restore integrity, professionalism and accountability has been exposed as nothing more than hollow words," said Angela Rayner, deputy leader of the main opposition Labour Party.

"Far from stopping the rot in Downing Street, he’s letting it fester."