Boris Johnson is being warned that embracing a disruptive no-deal Brexit would fuel nationalism in Scotland and risk the future of the union, as both opponents and supporters predict that he will now claim a decisive victory in the Tory leadership election.

Brexit must work for the whole UK to see off Scottish nationalism Read more

With Johnson seemingly weeks away from entering Downing Street, the Scottish secretary, David Mundell, issues a thinly veiled warning to him that Nicola Sturgeon would welcome a no-deal Brexit with “unseemly glee”.

Both Jeremy Hunt and Johnson have suggested they would be willing to back a no-deal Brexit if necessary. Yet, with signs that Johnson has retained a clear lead over Hunt, Mundell’s words appear squarely aimed at the former foreign secretary over his threat to leave the EU – with or without a deal – at the end of October. “Scotland has a first minister whose only true priority is the pursuit of independence,” he writes in an article for the Observer. “She poses as a defender of devolution while seeking to destroy it. She seizes on the problems of leaving the EU with unseemly glee. But it is easy to see why.

“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.”

Concerned figures across the party have already shifted from trying to stop Johnson’s ascent to Downing Street to restraining him once in office. An attempt to prevent him from suspending parliament in October, effectively stopping it from standing in the way of a no-deal Brexit, could be staged this week.

A group of Tories are preparing a bid to ensure they cannot be “locked out” of parliament, whoever wins the leadership, the Observer understands. They could attempt to launch the plan by amending a bill covering Northern Ireland this week. Johnson has refused to rule out suspending parliament but has said he is not attracted to the idea and does not believe it would be necessary.

Facebook Twitter Pinterest A no-deal Brexit would be a gift to Nicola Sturgeon in her push for independence, Mundell warns Photograph: Andrew Milligan/AFP/Getty Images

The move comes with MPs critical of Johnson reporting that a “radicalised” party membership has decisively opted to embrace his commitment to leave at the end of October. “The mood in the associations has hardened; it’s in the land of make believe,” said one influential MP. “Two-thirds of members seem to welcome no deal, and two-thirds of the country is opposed to it. Our members need to realise it is the country that will return the Conservatives to government, or Jeremy Corbyn. The extremes seem to be holding all the levers. That’s a big concern.”

As his leadership bid appeared increasingly unstoppable, many of Johnson’s highest-profile supporters were touring the country on Saturday urging members to cast their votes immediately for Johnson. The former Brexit secretary David Davis, who threw his support behind Johnson when Dominic Raab was eliminated in the early stages, said it was now clear that party members were rallying behind him as the man to deliver Brexit and see off Labour.

“The party is very clear. It is determined not to give the next election to Corbyn, and the best way to do that is to leave the EU before an election takes place. They have decided Boris is most likely to do that, and they are uniting behind him,” he said. Another Johnson supporter, the former cabinet minister Andrew Mitchell, said that if there were no upsets in the next few days, he should be home and dry, as by then most members would have returned their ballot papers. “It is not in the bag but it is his to lose. It is a case of getting through the next few days and then that will be that.” Mitchell told a “Back Boris” rally in the West Midlands that Johnson was a one-nation Tory with sound Conservative instincts on law and order, and tax, who would not only deliver on Brexit, and who would also “cheer us up”.

Another former minister, Crispin Blunt, said Johnson was heading for No 10. “While Jeremy Hunt has run a decent campaign it is not enough to overtake Boris, given the existing affection there is for him, and the sense that, given the challenges we face, we need someone exceptional.”

At a hustings in Nottingham on Saturday, Johnson won a standing ovation as he batted off accusations of bigotry and racism and presented himself as having a “deeply progressive” agenda. Asked by Amar Bhandal, 15, a Tory member, if he was “a fitting prime minister for everyone, including minority groups” after “derogatory and arguably racist comments in the past, for example about women wearing the burqa”, Johnson said the newspaper column in question was “a strong, liberal defence of the right of women to wear the burqa”.

Bhandal said: “I thought the response was a bit insufficient. He was trying to defend the comments he made by trying to argue that he was saying women should choose whether they wear the burqa, even though it was obvious from what he wrote that he wasn’t doing that.”

More evidence the Tories could receive a lift under a prime minister committed to an October Brexit comes in an Opinium poll for the Observer today. It shows a 5% swing in votes among Leavers from the Brexit party to the Conservatives, compared with a month ago. While languishing on only 23%, two points behind Labour which is on 25%, the Tories are up three points on last month’s tally.