Oliver Dowden has quit as Conservative chairman in the wake of the party’s double by-election defeat.
In a letter to Boris Johnson, he said “we cannot carry on with business as usual - somebody must take responsibility”.
He resigned barely an hour after the Tories lost the Wakefield by-election to Labour and Tiverton and Honiton to the Lib Dems.
Dowden said they were “the latest in a run of very poor results for our party”.
“Our supporters are distressed and disappointed by recent events, and I share their feelings,” he said.
“We cannot carry on with business as usual. Somebody must take responsibility and I have concluded that, in these circumstances, it would not be right for me to remain in office.”
Dowden had only been Conservative chairman since last September and had been one of the prime minister’s most loyal lieutenants.
His departure is yet another blow for the beleaguered PM, whose position will now come under fresh pressure from Tory MPs who fear their own seats are now at risk.
Johnson’s leadership was plunged into fresh crisis in the space of just five minutes at around 4am this morning.
First, Labour’s Simon Lightwood regained the Red Wall seat of Wakefield in west Yorkshire with a majority of 4,925 votes - a swing of 12.7 per cent.
If that were repeated at the next general election, it would be enough to give Starmer an overall majority.
Then, just moments later, it was confirmed that Lib Dem candidate Richard Foord had pulled off a stunning result in Tiverton and Honiton, overturning a 24,000 Conservative majority.
He won by 6,144 votes on an extraordinary 30 per cent swing away from the Tories.
It is the first time a governing party has lost two by-elections on the same day since 1991, when John Major was prime minister.
And it means Johnson has lost four by-elections inside a year, following the Lib Dem wins in North Shropshire in December and Chesham and Amersham last June.
Johnson, who is 4,000 miles away in Rwanda at a Commonwealth heads of government summit, yesterday rejected suggestions that he would have to quit if he lost both by-elections.
He said: “I’m going to be watching the results with interests but always full of optimism and buoyancy but most seasoned political observers know that by-elections in mid-term are never necessarily easy for any government.”
The by-election in Wakefield was called after the sitting Tory MP, Imran Ahmad Khan, quit after being convicted of sexually assaulting a teenage boy.
The Tiverton and Honiton by-election came after Neil Parish resigned as the Tory MP after he admitted watching porn in the Commons.