RISHI Sunak faces another potentially damaging by-election after a former Tory MP resigned with immediate effect following accusations of sexual harassment and cocaine use.

David Warburton has stood down from his seat of Somerton and Frome, hitting out in an exit statement at an “extraordinarily difficult” 14 months fighting “malicious allegations”.

He claimed he had been denied a fair hearing by the Independent Complaints and Grievance Scheme (ICGS) and prevented from “speaking out” while it probed the accusations.

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 judgement may at any time be freighted.”

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 that he harassed a female political aide in his Westminster flat.

The resignation will trigger an electoral battle in his Somerset constituency, adding to the problems faced by the Prime Minister amid the fallout from his predecessor-but-one stepping down.

Mr Warburton took the seat from the Liberal Democrats in 2015 and has a 19,213 majority but the party is already stepping up manoeuvres to reclaim it.

Lib Dem deputy leader Daisy Cooper said: “Time after time the Conservatives have mired themselves in sleaze and scandal neglecting the issues that really matter to people. Then they decided it was okay to leave local people in this seat without any proper representation at all.

“This by-election will be a clear contest between the Conservatives and the Liberal Democrats, Labour finished third last time and are completely out of the race. The people of Somerton and Frome need a local champion and they can have that at the next election by choosing our local Liberal Democrat candidate Sarah Dyke.”