Sir Gavin Williamson should be stripped of his knighthood if complaints against him are upheld, the Lib Dems have said.

The party is warning that the “serious allegations” against the former Cabinet Office minister risk “bringing the whole honours system into disrepute”.

Sir Gavin, who had already been twice sacked from the Cabinet in disgrace, bowed to pressure to resign as minister without portfolio on Tuesday after claims about his behaviour piled up.

They include allegations he sent expletive-laden messages to former chief whip Wendy Morton complaining about being refused an invitation to the Queen’s funeral, that he bullied a former official at the Ministry of Defence (MoD), and that he engaged in “unethical and immoral” behaviour while chief whip.

Sir Gavin said the claims against him were “becoming a distraction from the good work this Government is doing for the British people” and he was stepping back to “clear my name”.

The Lib Dems have written to the Forfeiture Committee – which advises on removing knighthoods – urging it to consider stripping the former minister of his title if he is found guilty of bullying.

If these complaints are upheld, he should be stripped of his knighthood, or else the whole honours system risks being brought into disrepute

Sir Gavin was only knighted earlier this year.

The party’s chief whip, Wendy Chamberlain, said: “The complaints being made about Gavin Williamson are extremely serious and suggest a bullying culture at the very top of the Conservative Party.

“If these complaints are upheld, he should be stripped of his knighthood, or else the whole honours system risks being brought into disrepute.

“Rishi Sunak appointed Williamson to Cabinet despite knowing of serious complaints about his behaviour. Since then he sat on his hands for days instead of taking action.

“The very least Sunak could do now is confirm he would support taking Williamson’s knighthood away if the investigations into his behaviour find him guilty.”

Ms Morton’s case has been referred to Parliament’s Independent Complaints and Grievance Scheme – as has, reportedly, that of the former MoD official. No 10 also launched an informal fact-finding exercise.

The Prime Minister’s press secretary said the matter of Sir Gavin’s knighthood would be one for the Forfeiture Committee.

Asked if Mr Sunak thinks he should lose the title, she said: “I believe there is a formal process for that called the Forfeiture Committee. And that would be a decision for them.”

A Labour spokesperson said: “I’m sure that the (Forfeiture) Committee would want to look at the conclusion of any investigation that there is.”

The Forfeiture Committee makes judgments on whether the honours system has been brought into disrepute.

It can recommend to the King, through the Prime Minister, that an honour such as a knighthood should be removed but is not itself an investigatory body.