Tory MPs have not been able to agree on very much since the momentous decision by voters to leave the EU. Yet as they headed back to their constituencies last week, there was one prediction that, for once, united them all. Figures from across the party agreed that Boris Johnson is odds-on to be the party’s next leader and to enter Downing Street. One cabinet minister, among those to have reluctantly accepted that view, had one word to sum up their feelings: “Gulp.”

Delight, anger and disillusionment were expressed by Tory MPs in anticipation that the former foreign secretary will finally grasp the crown he has coveted for so long.

Even among some of those backing his candidacy, there is an acknowledgment that they are taking a major gamble that could have serious implications not just for the party, but for the future of the UK.

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Johnson, who is currently poised to secure more than 70% of the membership’s vote according to current polling, on Saturday received a standing ovation at a hustings in Nottingham. He also received endorsements from the Times, the Telegraph and the influential ConservativeHome website.

For MPs concerned about his threat to leave the EU with no deal at the end of October, his clear lead has imbued a sense of determination. “I’ve had my period of mourning a long time ago,” said one. “It is going to be him. The key now is making sure we do everything we can to ensure that certain things can be stopped.”

Other party opponents are angry at Jeremy Hunt, the outsider for the job, for a campaign that “made it easy” for those with doubts about Johnson to back him. One minister pointed to “ill-judged remarks about business and hunting” for preventing him from building support. Hunt had to backtrack after suggesting he would allow a vote on scrapping the ban on foxhunting. He also said that he would willingly tell people whose companies went bust after a no-deal Brexit that their sacrifice had been necessary.

Hunt’s perceived lack of momentum has been accompanied by support for Johnson from surprising places. Several MPs point to the endorsements from the likes of Matt Hancock, the health secretary seen as opposed to no deal, and former minister Damian Green, previously regarded as one of the party’s leading Europhiles, as a sign that the party has decided to gamble that Johnson can deliver the electoral boost that his advocates claim he attracts. “Everyone has their own motives, reasons and agendas,” said one surprised MP, alluding to the age-old attraction of backing a winner.

Facebook Twitter Pinterest Damian Green and Nicky Morgan arrive for a meeting at the Cabinet Office in February. Photograph: Stefan Rousseau/PA

Can Johnson win back the votes of Leave voters currently attracted to Nigel Farage’s Brexit party? The latest Opinium poll for the Observer suggests a 5% swing in votes among Leavers from the Brexit party back to the Tories. Johnson also has a clear supporter base: 53% of “diehard Leavers” think he would make the best prime minister. Two thirds (64%) of “diehard Leavers”, and 42% of all UK adults, believe that Britain will leave the EU within the current deadline if he becomes prime minister. Yet the poll still puts the Tories in second place, two points behind Labour, with the Brexit party netting an ominous 22% of the vote.

Away from Johnson’s vows on Brexit, there are two major issues causing concern across the party. The first is a criticism that has been aimed at both candidates – new spending commitments totalling tens of billions of pounds. A tax cuts splurge, totalling some £20bn, combined with a pledge to increase school funding that could come at an even bigger price have concerned both MPs and party donors that the Tories’ most reliable attack line against Labour – that it cannot be trusted with the economy – is at risk. As one major donor put it: “What can one expect when the whiff of power is overwhelming and common sense thrown to the wind?”

Nicky Morgan, the Tory chair of the Treasury select committee, is more withering. “The Conservative party traditionally has a reputation for economic competence which is hard won and easily lost,” she said. “Frankly, both Boris Johnson and Jeremy Hunt have been in cabinet. They have seen how hard it has been to get the public finances back into some sort of balance. They can’t keep spending £26bn over and over again, which is what we would expect to see from Jeremy Corbyn’s Labour party.”

The other flashing red light is the future of the UK and the risk posed by the kind of no-deal Brexit Johnson says he is willing to embrace. Talk privately to Tories engaged in Scottish politics and it is clear that they know Johnson could end up being a gift to Nicola Sturgeon and the SNP – a bogeyman used to mobilise an electorate that voted Remain. However, it is a sign of Johnson’s level of support that some Scottish Tory MPs are openly backing him. Johnson has been trying to improve his image in Scotland and has already apologised for an old article in which he suggested government by a Scot was “just not conceivable”.

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Writing for the Observer, David Mundell, the Scottish secretary, makes clear that a no-deal outcome would boost nationalists, in a not-so-coded message to Johnson: “A difficult no-deal Brexit would not only damage our economy, it would fuel nationalist claims of a UK that is insensitive to Scotland’s needs. The new prime minister faces considerable challenges, and the future of the UK is high on the list.”

For MPs opposing Johnson’s Brexit plans, attention has turned from stopping his administration to restraining it once in office. This week, a group of MPs will try to prevent Johnson from suspending parliament as a route to securing a no-deal Brexit that most MPs oppose. The plan, set to be unveiled as an amendment to a Northern Ireland bill tomorrow, is a sign of the determination of some to limit the room for manoeuvre of a Johnson premiership.

Opponents are in desperate search of reasons to be cheerful. “We could be providing him with a ladder to climb down,” said one. “If he was able to blame other people [for stopping a no-deal Brexit], that would allow him to be the more sensible and pragmatic person that one hopes he would be.

“That’s my optimistic take. I need that, or I’ll just cry.”