Somerton and Frome MP formally quits
David Warburton has criticised the investigation into alleged wrongdoing
The MP for Somerton and Frome has formally quit after an investigation into allegations of sexual harassment and cocaine use.
The decision means Rishi Sunak faces another potentially difficult by-election in the seat vacated by former Tory David Warburton.
Mr Warburton's exit from the Commons was confirmed by the Treasury following his appointment as Steward and Bailiff of the Manor of Northstead - one of the procedural routes for an MP to quit.
In an interview with the Mail on Sunday, Mr Warburton admitted to taking cocaine after drinking "tons of incredibly potent" Japanese whiskey, but denied claims he harassed a female political aide in his Westminster flat.
Mr Warburton's resignation will trigger an electoral battle in his Somerset constituency, adding to the problems faced by the Prime Minister who faces at least two other by-elections after the resignations of Boris Johnson and Nigel Adams.
He took the seat from the Liberal Democrats in 2015 and had a 19,213 majority.
When he announced his resignation on Saturday, Mr Warburton hit out at the investigation conducted by Parliament's Independent Complaints and Grievance Scheme (ICGS), claiming he had been denied a fair hearing.
In his resignation letter he said had been left with "no choice" but to provoke "the upheaval of a by-election", adding: "It is my hope that, in so doing, I can freely illuminate the methods of an oversight system not fit for purpose, so that friends and colleagues in the House can see the perverted process by which their own judgment may at any time be freighted."
A House of Commons spokesman said: "Parliament remains absolutely committed to the ICGS.
"It is there to ensure that all complaints are dealt with in a manner that is fair, thorough, independent and efficient, offering support to all parties.
"The target to reduce the length of investigations must always be balanced against the paramount requirement to ensure that investigations are rigorous and robust.
"The scheme always seeks to learn from cases, and is mindful of the impact investigations may have on those involved."
The spokesman refused to be drawn on Mr Warburton's specific case as confidentiality requirements meant "we cannot provide any information on any complaints or cases, including whether or not a complaint has been received".