Senior Tories are warning Liz Truss that she will lead a deeply divided Tory party to inevitable defeat at the next election unless she makes a concerted effort to include senior figures from across the party – including critics of Boris Johnson - in her cabinet. The foreign secretary is expected to be named on Monday as the new Tory leader and then enter Downing Street as prime minister on Tuesday after visiting the Queen at Balmoral. But after a bruising and at times hugely divisive seven-week campaign against former chancellor Rishi Sunak, senior figures in the party fear she may be about to pack her administration with a mix of Johnson loyalists and rightwingers such as John Redwood and Iain Duncan Smith, inflaming tension with moderates. On Saturday night a former Tory cabinet minister and critic of Johnson said there would be huge and “explosive” consequences if Truss allies such as Duncan Smith and Nadine Dorries were appointed to top positions and then tried to use their influence to scrap a parliamentary inquiry into whether Johnson deliberately misled parliament. Duncan Smith has put his name to a parliamentary motion calling for the investigation by the privileges committee – which could lead to Johnson being suspended as an MP – to be “discontinued”, while Dorries has made clear she backs such a move. The privileges committee has been given the task of establishing whether Johnson deliberately misled parliament by denying knowledge of lockdown-breaking parties in Downing Street. The former cabinet minister said: “If she wins, then on policy issues, including budget issues, most colleagues will take the view that she deserves the chance to put her plans into effect. She will get things through parliament. But if her government tries to do things on the integrity questions, I think there could be trouble quite early on. That would be explosive.” The tension of Johnson’s past behaviour is one indication of how his presence may hamper Truss as she tries to keep his allies happy while governing the country at a time of deepening economic crisis. Another former cabinet minister and Johnson critic, David Davis, said that because Truss would have won the keys to No 10 with the support of less than a third of Tory MPs, it was vital that she unite the parliamentary party with a “big tent” approach to the formation of her government. “It is incredibly important that the incoming leader knits the party together. It was one of Boris’s earliest failures that he did not do that. He just picked the loyalists and as a result it made it more and more difficult to manage the party. “It is not just in the party’s interests but in the interests of delivering serious policy and winning the next election. None of those are possible with a divided party.” Amanda Milling, a Foreign Office minister and former party chair, said: “This leadership contest has been toxic and bruising for the Conservative party brand. As it concludes, the whole party, from the frontbench to the backbench, has to come together as one united team in order to deliver for the British people and defeat Labour. If we don’t, we risk being out of power for a decade.” Tory MP Kevin Hollinrake, a member of the Treasury select committee, who still believes Sunak may triumph and has put bets on him to do so, said the party had to win back a reputation for competence and unity over the next 18 months or face defeat and not dwell on past divisions. He said: “We are not going to win the next election with a divided party so it is absolutely vital that whoever wins brings people in from different camps.” As well rewarding Johnson loyalists such as Duncan Smith, Redwood and Jacob Rees-Mogg, Truss is expected to offer top jobs to her key backers Kwasi Kwarteng, Suella Braverman, James Cleverly and Thérèse Coffey, while pushing out those who failed to support her, including health secretary Steve Barclay and environment secretary George Eustice. A senior minister predicted early rebellions unless Truss adopted a big tent approach. “If she does what is rumoured and brings back Redwood and Duncan Smith, there’ll be hell to pay. You’ll have senior people on the backbenches joining forces, dishing out tempting amendments to the budget and all of that sort of thing, prising the red wall MPs away from her. “It will be absolute mayhem, unless she makes a really concerted effort to dip into all the different factions that make up the party. If she doesn’t do that, I think this could be a really, really difficult time for her and therefore for us.” Former chief whip Mark Harper said that given divisions within the parliamentary party “whoever wins would be well advised to appoint a broadly based cabinet and government drawing on talent from across the parliamentary party so that we can create a more cohesive feel and that can work together to get us through what is going to be a very difficult autumn, winter and new year.” MPs said they were expecting an “absolutely massive package” of help to be announced by Truss in the opening few weeks of her leadership, despite her claims during the recent campaign that she opposed what she regarded as “handouts”. One MP said there was talk of aid running to many tens of billions, paid back by the state over a long period. Despite the expectation of a clear win for Truss, polling for the Observer finds that she has actually lost ground among Conservative voters as the leadership contest has progressed. Among those who voted Conservative in 2019, the net proportion believing Truss “gets things done” was 26% in July. That has now fallen to 5%. The net proportion seeing her as a “strong leader” has fallen from 13% to -4%, while the net proportion seeing her as a prime minister in waiting has fallen from 5% to -11%. It will be seen as a sign that she has been propelled to the leadership by the early momentum she gained in the contest, after backing tens of billions in tax cuts. While some of Sunak’s closest allies still believe the contest is extremely close, with some late voters splitting in his favour, Truss is the overwhelming favourite. Ryan Shorthouse, chief executive of the Bright Blue thinktank, said: “If she just surrounds herself with the Boris fan club, puts in place a continuity cabinet with the same old faces and uses the same arguments, policies and tactics as Johnson, she will lose the confidence of the parliamentary party rapidly. The public will feel nothing has changed.” On Monday, the 60-strong One Nation group of Tory MPs will meet in the House of Commons to discuss how to react to the result of the leadership contest. Tory moderates fear that Truss may try to stamp her mark on the leadership with moves to suspend the Northern Ireland protocol and perhaps even remove the UK from the European court of human rights. “That will be a touchstone for a number of people,” said a senior figure. “If she goes down that path there will be trouble. All the indications are that she will not be very inclusive. I expect that she will offer Rishi something in the hope and expectation that he will refuse but otherwise I think it will be her people.”