British minister Gavin Williamson resigned late Tuesday from new Prime Minister Rishi Sunak's government following allegations he sent menacing messages to lawmakers and former colleagues.

Williamson came under increasing pressure since the emergence of a series of expletive-laden text messages allegedly sent by him to Tory colleague and former chief whip Wendy Morton.

They said she was seeking to "punish" MPs out of favour with then-premier Liz Truss by excluding them from Queen Elizabeth II's funeral, warning: "There is a price for everything."

On Monday a senior civil servant told The Guardian newspaper Williamson had bullied them and told them to "slit your throat".

"As you know, there is an ongoing complaints process concerning text messages I sent to a colleague. There have been other allegations made about my past conduct," Williamson said in his resignation letter.

"I refute the characterisation of these claims, but I recognise these are becoming a distraction for the good work this government is doing for the British people.

"I have therefore decided to step back from government so that I can comply fully with the complaints process that is underway and clear my name of any wrongdoing," he wrote.

Williamson, 46, was sacked twice as minister in the past by former premiers Boris Johnson and Theresa May.

Sunak meanwhile said he would not be "passing judgment" until after an "independent complaints investigation".

"I want to see the results of that, obviously, but I've been very clear that language is not right, it's not acceptable," British media quoted Sunak as saying.

Downing Street and the Conservative party have launched investigations into the claims.