Penny Mordaunt came within 10 MPs of making the ballot against Rishi Sunak, with her allies blaming Boris Johnson for spooking Conservative MPs who told her they had no choice but to try and block his return. Sources in Mordaunt’s campaign team showed evidence that Mordaunt had almost reached the requisite number of endorsements to face Sunak in a run-off, but admitted that support began to drain away in the final hours. One of Mordaunt’s key backers, the former minister George Freeman, broke ranks in the final hour before the announcement and urged her to back Sunak. “Penny Mordaunt is a huge force for Conservatism; with the life-story, vision and courage to help lead a Conservative revival,” he tweeted. “I’m proud to support her. “But given the urgent need for Conservative stability and unity this week, I’m urging her to join and back Rishi Sunak today.” Mordaunt’s campaign also hit the buffers when she failed to secure the endorsement of either the European Research Group of Brexit-backing MPs or the One Nation group of moderates. Damian Green, the latter group’s chair, had backed Mordaunt but the statement put out by the caucus on Monday resolved only to give the new prime minister full support. In a tweet announcing she had not made the ballot, Mordaunt said: “These are unprecedented times. Despite the compressed timetable for the leadership contest it is clear that colleagues feel we need certainty today. “They have taken this decision in good faith for the good of the country. Members should know that this proposition has been fairly and thoroughly tested by the agreed 1922 [Committee] process.” There was some bitterness among both Sunak and Mordaunt supporters about how the final hours of the brief campaign had played out. One Mordaunt-backer was scathing about Freeman’s change of heart, comparing him to Nadhim Zahawi, the cabinet minister who had written an op-ed backing Boris Johnson, just as the former prime minister backed out of the race. “Everyone can see it for what it is, you win more respect for sticking by your principles,” they said. Inside Mordaunt’s camp, her allies said her campaign was stymied by MPs’ fears about a return for Johnson. Insiders say Mordaunt believes she has never been tested in a fair fight, amid allegations of dirty tricks in the first leadership election, where she was overtaken by Liz Truss in the final ballot. This time, her allies say, Mordaunt was hampered by a Johnson campaign that sent fearful MPs over to Sunak. “People were saying they had to back Rishi to make sure we didn’t get Boris,” one insider said. “And then of course Boris doesn’t even run in the end. Both times she has been stitched up.” Outside Sunak’s address to MPs, Mordaunt told reporters she was doing well and was “here to support the next prime minister”. Her arrival was greeted with banging of desks and cheers, and MPs kissed her on the cheek, alongside her campaign manager, Andrea Leadsom. Mordaunt has been tipped for a key role in Sunak’s cabinet – perhaps as foreign secretary – but some Sunak-backing MPs said they believed she had pulled out too late. “She didn’t have the numbers; in the last half an hour it was getting to the point where people were asking what she was playing at,” one MP said. Another says Mordaunt had an “eye to the next contest, trying to demonstrate to members that she was thinking of their interests”.