Rishi Sunak will lead the Conservative party into an election at the end of the year despite reports of rebellious MPs plotting to oust him to avoid wipeout at the polls, a senior cabinet minister has said. Mark Harper, the transport secretary, told his fellow MPs to “have some confidence” in the party leadership, insisting Sunak was focused on “making the right decisions” for the country. Many backbench Tory MPs are increasingly concerned about losing their seats after a torrid week for the prime minister, with his budget failing to deliver an immediate bounce in the polls, the defection of Lee Anderson to Reform, and the party embroiled in a racism row over its biggest donor. There has been speculation in recent days that some MPs on the right of the party want Penny Mordaunt, the leader of the Commons, to act as a “stalking horse” candidate to trigger a leadership contest before the next general election. Asked whether Sunak would still be Tory leader at the election, Harper told Sky News’s Sunday Morning With Trevor Phillips programme: “Yes he will. He will take us into that election and he will set out very clearly that we’re a government with a plan. I’m going to be supporting him all the way through, and I’m confident that my colleagues will.” According to private polling seen by the Mail on Sunday, the Tories are heading for the worst defeat in their history. The seat-by-seat research, which the newspaper said was conducted on behalf of corporate businesses, suggests Labour could be on course to win 250 seats and the Conservatives fewer than 150. That would be fewer than the 165 the Tories won in 1997 and the 156 in 1906’s Liberal landslide. Even the best-case scenario for the Tories indicates a 50-seat Labour majority. Harper urged anxious colleagues to stay the course, telling them that “politics is a team game”. He said: “What I would say to all of my colleagues is this: I spend my time as transport secretary focusing on doing what I think is the right thing for the country, making decisions that I think are sensible. That is the approach that the PM takes as well. He focuses on making the right decisions.” Mordaunt made no public comment about the claims but her supporters said she was not party to, or aware of, any plot, and that she believed the stories were an attempt by rightwing rivals to damage any challenge she may make in future. Several Tory MPs maintain that Mordaunt has been “on manoeuvres” for months, making clear she would be happy to visit MPs’ constituencies and get to know their local party officials. Sunak has ruled out holding a general election on 2 May, the date of the local elections, and has previously indicated he will send the country to the polls this autumn. Labour and the Liberal Democrats, who had talked up the prospect of a May vote, have accused the prime minister of “bottling” it and of “squatting” in No 10. Harper said: “The prime minister made it quite clear at the beginning of the year that his working assumption was the election was going to be at the end of the year. All this sort of froth we’ve had about an election being in May was always nonsense, frankly, and he made that clear at the beginning of the year.” Jonathan Ashworth, the shadow paymaster general, called on Sunak to name the election date. “There’s Tory MPs who are in the papers today saying Rishi Sunak can’t continue,” he said. “This is not in the national interest any more. It is irresponsible. We need stability in this country. He could stabilise this by calling, naming the date of, a general election. Otherwise I fear we may have a Tory leadership election ahead of a general election.”