A fourth Conservative MP has resigned in less than 10 days, triggering a fourth by-election for Rishi Sunak.

David Warburton – accused of sexual harassment and drug abuse – resigned last night, triggering a by-election in his Somerton and Frome constituency.

The 57-year-old MP was suspended from the party in April 2022 pending the outcome of an Independent Complaints and Grievance Scheme (ICGS) investigation into the allegations.

What has Mr Warburton said about the IGCS?

In his resignation letter, Mr Warburton claimed he had been denied a fair hearing by the ICGS and prevented from “speaking out” while it probed the claims.

Mr Warburton said the “malicious allegations” and “flawed” 14-month investigation had “inflicted unimaginable and intolerable destruction on my family and on me”.

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.”

He claimed the ICGS “prevented” him from speaking out and that it “moves at a cripplingly glacial pace towards a predetermined conclusion”.

What has parliament said in response to the claims?

The House of Commons has pushed back on Mr Warburton’s claims, and does not accept that the ICGS is not fit for purpose.

A House of Commons spokesperson 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.”

They said that any aim to reduce the length of investigation “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,” they added.

There is ongoing work to ensure “transparency and confidence” in the process, and the spokesperson added: “Combined with oversight and appeal functions delivered by the Commissioner for Standards and the Independent Expert Panel, we now have strong, fair and independent processes in place that we encourage all those in parliament to use if needed.”

Sky News political correspondent Ali Fortescue explains more about David Warburton, why he has resigned, and what this means for Rishi Sunak: