British Prime Minister Boris Johnson is facing the growing threat of a confidence vote as two more lawmakers suggested they had lost faith in his government over the "partygate" scandal and a former party leader said he could be challenged next week.

Compounding the pressure, Johnson's ethics adviser said the prime minister may have broken the ministerial code when he was fined by the police over a birthday party in June 2020 when indoor socializing was banned. Ministers who breach the code are normally expected to resign.

John Stevenson, a Conservative member of parliament, said he has been "deeply disappointed" by the rule-breaking parties during the COVID-19 national lockdowns and called for the prime minister to put himself forward for a vote of confidence as a way to "draw the line" under the issues.