Another Conservative MP has stepped down from his role as the row grows over Sir Bernard Jenkin attending a party during the pandemic.

David Warburton quit as he revealed he was denied a fair hearing by a parliamentary harassment watchdog looking into allegations he made unwanted advances to two women. His decision will trigger another by-election for Rishi Sunak, the Prime Minister.

It meanwhile emerged that leaked WhatsApp messages showed that Sir Bernard had thrown a lockdown drinks event for his wife. The Tory grandee held former prime minister Boris Johnson to account over Partygate in his role on the Commons Privileges Committee, which Mr Johnson branded a “witch-hunt”.

Mr Warburton has denied the harassment claims but admitted taking cocaine after drinking “incredibly potent” Japanese whisky with a third woman, The Mail on Sunday reports.

He claimed she secretly filmed and photographed him following a late-night House of Commons vote.

Mr Warburton said: “I was set up, but I have been naive and incredibly stupid.”

Daniel Greenberg, the Parliamentary Commissioner for Standards, accepted the claims of a political aide made against the MP.

A Conservative Party spokesman said: “The Independent Complaints and Grievance Scheme is an independent body set up by Parliament and the Conservative Party respects its processes. Mr Warburton had the whip withdrawn over these complaints last April and has not sat in Parliament as a Conservative since.”

The Prime Minister now faces four potential by-elections with two contests in Uxbridge and South Ruislip, and Selby and Ainsty already scheduled for July 20 after Mr Johnson and his ally Nigel Adams resigned.

Nadine Dorries, who had also announced she was going to quit over the fallout from the former prime minister’s resignation honours, is staying while she seeks to investigate how she was denied a seat in the Lords on the list.