Senior Tories are engaged in a frantic campaign to stop Boris Johnson staging a dramatic return to Downing Street, with claims he would cause further economic damage and risk “the end of the Conservative party”. Johnson’s team was claiming on Saturday night that he had privately secured the support of the 100 MPs necessary for entering the race, despite only 55 backing him in public. The assertion was immediately disputed by MPs and rival leadership campaign sources. Johnson released a photo of himself lobbying an MP on the phone, but his allies on Saturday night could not confirm he would officially enter the contest to win back the leadership he was deposed from just months ago. In another day of high political drama in the race to succeed Liz Truss as prime minister, supporters of frontrunner Rishi Sunak were attempting to secure support from MPs so overwhelming that Johnson would be forced to drop out. They believe a final indicative vote among MPs overwhelmingly backing Sunak would send a message to members not to lumber them with another leader they do not support. The two frontrunners held talks on Saturday night as they approached Monday’s 2pm deadline for nominations and while neither camp disclosed the content it is understood that Johnson was proposing a deal which he claimed would avoid a divisive battle in the party. Former cabinet ministers backing Sunak said a comeback for Johnson would also unsettle the financial markets, increasing the risk of further sharp rises in interest rates by the Bank of England within days. One former cabinet colleague of Johnson said desperate efforts were under way to rally support behind Sunak, not least because he would symbolise stability to the financial markets and reduce the chances of interest rates and mortgages rising further. He said that the medium-term fiscal plan due to be announced by chancellor Jeremy Hunt on 31 October would be vital and must not be compromised by Johnson’s return. “It’ll then be a question of whether Johnson puts his narcissism above the interests of the country,” said a senior source. “A big win for Sunak will put pressure on Johnson.” Kemi Badenoch, seen as a future leader, provided Sunak with a big boost by backing him. Meanwhile, there were claims that a hardcore group of about a dozen MPs opposed to Johnson’s return would resign the whip should he take over again. Other Tory MPs said Johnson would struggle to get any laws through parliament should he return, given the strength of feeling against him. One former minister said: “It would be the end for me. I know others who feel the same. The party has already left us behind. If Johnson returned, I would find it impossible to continue.” Tory MP Roger Gale revealed on Saturday that he would resign the Tory whip if Johnson became prime minister once again. Another Tory MP said they would consider their place in the party should Johnson return, warning it was the one outcome that risked precipitating an early election and could spell “the end of the Conservative party” should MPs begin to split away. Several Tories made clear that the privileges committee investigation into whether Johnson misled MPs over Partygate made it impossible to accept him as leader. Some said they would back an election rather than vote for any attempt to spare Johnson from the inquiry. A Commons source said the evidence and public testimony could “finish him off” politically, before the new year. It was not only Tory MPs on the moderate and One Nation wings of the party who were urging Johnson not to stand. David Frost, a former Brexit minister and close ally of Johnson, called on his party colleagues in the Commons to back Sunak. The Tory peer tweeted: “Boris Johnson will always be a hero for delivering Brexit. But we must move on. It is simply not right to risk repeating the chaos and confusion of the last year. The Tory party must get behind a capable leader who can deliver a Conservative programme. That is Rishi Sunak.” Former Daily Telegraph editor Charles Moore, who is a friend of Johnson, also urged him not to stand, saying it was too early to return and that Sunak had been proved right about unfunded tax cuts. Moore urged Johnson to “sit this one out”. Such is the speed and unpredictability of the contest that some MPs were predicting on Saturday night that Johnson could even end up endorsing Sunak, the man he actively helped to block from the leadership. However, there are concerns that the party will still descend into warfare even if Sunak takes the helm. On Saturday night, Tory MPs were openly questioning the Johnson campaign’s claim that he had 100 backers. Robert Syms, the Conservative MP for Poole, said: “If Boris has 100 in the bag, why is his campaign putting out pics of him begging for votes?” Meanwhile, the third contender in the race, Penny Mordaunt, was also struggling for public backers. Her team said that more supporters would be unveiled over the weekend. It also believes she could benefit hugely should Johnson pull out of the race early, as many of his backers will want to stop Sunak at all costs. Johnson is still likely to win support from MPs in the pro-Brexit European Research Group, which is meeting on Monday morning to discuss the leadership contest. Senior figures in the group are still predictingthat Johnson could secure the support of 100 MPs needed to officially enter the race. The latest Opinium poll for the Observer put Labour on 50%, 27 points ahead of the Conservatives (who are down 3 points from a fortnight ago). The Conservatives are on 23%, the Liberal Democrats are on 9% (down 2 points) and the Greens remain unchanged on 6%. The poll shows the Tories have now lost many of the 2019 voters won when Johnson secured a massive 80-seat majority. It reveals that 30% of Tory voters at the 2019 election have switched to Labour.