If nothing else, the revolt showed that lawmakers' loyalty to Johnson is heavily conditional on his reputation as a vote-winner, and that that reputation is in severe jeopardy.

Next week, a civil service report is expected to be published on a series of gatherings that appeared to fly in the face of coronavirus lockdowns and have already battered Johnson's standing among voters - and that could be the cue for more seasoned and formidable rivals to move against him.

Many of the rebels were elected as first-time MPs in 2019 by constituencies that had not voted for the Conservatives for decades, and felt they owed those surprise victories to Johnson.

But dissent had been growing for months before the rebels met twice early in the week to gauge the appetite for trying to force Johnson out, according to lawmakers, some of whom attended the meetings. All asked to remain anonymous.

They agreed to start the process of forcing a parliamentary no-confidence vote against Johnson, who is under huge personal pressure over revelations about gatherings at his official Downing Street premises, and has urged critics to await the outcome of civil servant Sue Gray's investigation. read more

One of the new MPs said they had been struggling with the direction of the party and Johnson's government since November. With the steady drip-feed of reports of lockdown-breaking parties in Downing Street, they became bolder.

Some were frustrated at having to vote for policies they disagreed with, some felt Johnson's administration was failing to engage with Conservative MPs, and many were angry at how missteps, scandals and policy were being dealt with.

Johnson has repeatedly said no COVID-19 rules were broken at Downing Street, but did apologise for attending a gathering on May 20, 2020, for which staff had invited by one of his aides to "bring your own booze".

"OVEREXCITED"

One disgruntled lawmaker described Johnson's responses to the allegations, including his argument that he was not aware the event was anything other than a work meeting, as "bullshit".

By Tuesday, some thought they might have collected enough support to pass the 54 written expressions of discontent needed to trigger a vote of no-confidence in Johnson in the parliamentary party.

But their plot was flawed. They failed to agree on a successor, did not work out a game plan to gather the numbers they lacked, and were confronted by a party machine that undermined their attack, the sources told Reuters.

Within a day, it became clear that the threshold of 54 letters had not been met. A few hours later one of their colleagues, Christian Wakeford, quit the Conservatives to join the opposition Labour Party.

Several older Conservatives were less than surprised when the plot failed.

One veteran Conservative MP who has been involved in training potential candidates said the new intake had not been hardened by the experience of previous unsuccessful campaigns to get elected.

In addition, the fact that much of their parliamentary work has been conducted virtually, because of coronavirus restrictions, means they have missed out on a more usual initiation into their parliamentary party and the work of an MP.

"When they are getting emails and letters from disaffected voters, some of whom would never vote Tory (Conservative) anyway, they are getting spooked," said one senior Conservative lawmaker, adding that the new cohort did not know enough other older members in parliament from whom to seek advice.

"They are all a bit overexcited," said another senior Conservative.

But "overexcited" is not the same as "wrong". Sue Gray's civil service report is awaited more keenly than most.