Sunak, who took office late October as Britain's third prime minister in two months, has also faced criticism for re-appointing Suella Braverman as interior minister just days after she was fired by his predecessor for security breaches.

Williamson said late on Tuesday he was stepping down after media reported that colleagues had accused him of bullying, with one saying he told a government official to "slit your throat".

Williamson, who has been fired from other ministerial roles twice in the last four years, said he was complying with a complaints process and he refuted the characterisation of the messages.

Sunak said he accepted Williamson's resignation with "great sadness".