An increasing number of top Conservatives are calling for Boris Johnson to step down as Tory leader and prime minister "sooner rather than later," without waiting for a clear successor to emerge.

High-ranking MPs are encouraging hesitating colleagues not to delay due to worries regarding the succession, but rather to strike before it is too late.

One former minister told the Observer: “Things have changed. There is now a feeling that we can’t defend what is going on and that we can’t delay any longer because of the succession or Ukraine. If we don’t act well before the party conference in October, it will be too late.”

Following another disastrous week for Johnson, during which MPs from all parties agreed to launch their investigation into whether he purposefully misled parliament, MPs say that several potential successors, including Liz Truss, Penny Mordaunt, and Jeremy Hunt, are ramping up campaign preparations and canvassing support.

Last night, the former Tory chief whip, who last week called for Johnson to go, told the Observer he understood why some colleagues wanted to delay acting until after Partygate investigations were complete, or for other reasons.

But he urged them to have confidence that an excellent successor would emerge during the process to elect a new leader, even if it was unclear now who that would be.

“I have seen enough to conclude that the prime minister needs to go,” Harper said. “My colleagues can be confident that we have very talented people and a very robust process for selecting a new leader that will ensure we get a capable, credible successor who can set out an attractive proposition and ensure we can win the next election.”

He added: “I think the facts will mean that a majority of Conservative MPs will conclude that the prime minister needs to go.”

'A broomstick would be better'

Another former cabinet minister said doubts over the succession were now irrelevant, such was the urgency of the situation. “A broomstick would be better than what we have at the moment,” he said.

The mood swung dramatically against Johnson last week after he was forced to apologize to the Commons for being fined for attending a lockdown birthday party in 2020 and then appeared to back attempts to order his MPs to block an investigation into whether he had deliberately misled parliament by previously denying parties had taken place. 

Many Tory MPs are waiting until the results of the 5 May local elections before deciding whether to send a formal letter of no confidence in Johnson to the chair of the backbench 1922 Committee, Graham Brady. If Brady receives 54 or more such letters, a vote of confidence has to be held, and if Johnson loses he must step down.

The problems that have recently engulfed the previous favorite to succeed Johnson, chancellor Rishi Sunak – over his wife’s tax affairs, and the fact that he, too, was fined for breaking lockdown rules – are seen as having destroyed his chances of following Johnson into No 10.

Read more: Johnson's leadership in turmoil after new Partygate reveal

Johnson insisted during a two-day trade trip to India that he would lead his party into the next general election. But the Partygate scandal dogged him throughout the visit. Shortly before his return to London on Friday, it emerged that the Metropolitan police had started to issue fines for another party he attended – in this case a “bring your booze” garden event on 20 May 2020. No 10 said Johnson had not been fined for attending the event, though it was impossible to say whether he would be in the future.

Opposition party leaders said it would be unacceptable for the prime minister to hold back information about whether he had been fined ahead of the local elections.