Rishi Sunak has won the backing of the leading Eurosceptic Steve Baker, who warned that Boris Johnson returning as prime minister would be a “guaranteed nailed-on disaster” that would cause the government to implode. Sunak, who is the frontrunner to succeed Liz Truss, has now far exceeded the necessary 100 MPs to get on the ballot. Johnson appears to be struggling to reach that threshold despite the claims of his supporters, although on Sunday he won the backing of Nadhim Zahawi, the seventh cabinet minister to join his side. Jacob Rees-Mogg, the business secretary, said Johnson was “clearly going to stand” and the “people doing the numbers tell me they have the numbers”. Sunak’s campaign received a further boost on Sunday as he won the backing of Baker, a former Truss supporter, minister and influential figure in the European Research Group faction. He told Sky’s Sophy Ridge on Sunday: “I think it would be for the best if Boris did something big and statesmanlike. I mean, if he wants to come back as prime minister, he would need to do it after this privileges issue is settled. I think he’d make an amazing chairman of the party … “But what we can’t do is have him as prime minister in circumstances where he’s bound to implode, taking down the whole government with him. We just can’t do that again.” Sunak and Johnson spent Saturday night locked in talks over their potential future roles in the party. Johnson’s camp has been pushing for a rapprochement following Sunak’s resignation, which helped trigger the former prime minister’s exit from No 10, but their meeting appeared to end without a deal. One of Johnson’s leading supporters, Chris Heaton-Harris, said Johnson “has the numbers” to win but he could not say why neither he nor Sunak had not publicly declared. The third candidate is Penny Mordaunt, the leader of the Commons, whose supporter Damian Green warned against a “stitch-up” by big figures in Westminster without a vote going to Tory party members. Speaking on Sky News, Green said of Johnson: “We saw what happened last time and how the government literally fell apart. We know there’s this investigation going on and as long as that’s going on if [Johnson] became leader there’s the possibility that we could all be here again.” Mordaunt told the BBC’s Laura Kuenssberg that she believed she could bring the party together. She denied she had been in touch with Johnson’s camp offering her support in return for a job – and said she was not contemplating backing another candidate. Many Conservative MPs remain extremely worried about the prospect of a Johnson comeback, with ongoing questions over Partygate and the threat of defections by some MPs who have indicated they will refuse to work with him. Baker highlighted the forthcoming inquiry into whether Johnson misled the House of Commons over the Partygate scandal, saying MPs will “refuse, as they see it, to lay down their integrity to save him, and at that moment his premiership will collapse”. Baker declined to say which way he would vote on this issue, adding that the idea of a Johnson premiership would be “a guaranteed nailed-on failure and we cannot allow it to happen”. He also delivered a warning to Sunak that he would not hesitate to join with other Eurosceptics if he did not carry on with the government’s current policy on the Northern Ireland protocol.