After months of speculation about the rift between Ruth Davidson and the man likely to be named prime minister next week, the Scottish group of MPs will assure Mr Johnson that he will have their support if he wins the leadership.

But they will press for reforms of Whitehall to enhance the Union, and for Scots to be appointed to key ministerial roles and as advisers in Downing Street.

“We will be making a pledge of loyalty,” a senior Scottish Tory source said. “The key thing is that he listens.”

Conservative leadership candidate, Boris Johnson is seen arriving at a Westminster address on July 16, 2019 in London, England. (Photo by Luke Dray/Getty Images)

Referring to controversies over Mr Johnson’s personal life, and his closeness to US president Donald Trump, the source added: “What we’ve seen during this leadership contest is what it’s going to be like with Boris in Downing Street.

“There will always be something happening every day. It’s about what else he does around that, and throughout the campaign on Scottish issues he has been remarkably on message.”

David Mundell, who appears increasingly likely to keep his job as Scottish secretary despite previously suggesting he would not serve in Mr Johnson’s Cabinet, will be at the meeting. In total, at least nine MPs are expected to attend, compared with just five who went to an earlier meeting with the challenger for the Tory leadership, Jeremy Hunt.

Mr Johnson has already signed up to a “manifesto” of demands from the whole Scottish Tory group at Westminster, which called for direct UK government investment in devolved areas of responsibility, reforms to put the Union at the heart of government decision making, and a flexible post-Brexit immigration system that supports key Scottish industries.

Mr Johnson will be asked for clarity on plans to name himself “minister for the Union” to ensure that policy decisions work for all parts of the UK, and reforms to Whitehall departments, including a possible expansion of the Scotland Office, which could see one of the new Scottish Tory MPs given a ministerial job for the first time.

“There has been speculation about the shape of the Scotland Office,” one Scottish MP said. “There’s a strong desire for there to be a junior minister drawn from the Commons.”

SNP MP Tommy Sheppard said the support for Mr Johnson from Scottish Tory MPs was “embarrassing, shameful and utterly unforgiveable”.

“This craven ‘pledge of loyalty’ to Boris Johnson is the ultimate humiliation for Ruth Davidson, whose authority and status is now shattered beyond repair,” Mr Sheppard said. “It speaks volumes that rather than standing up for the people of Scotland, Scottish Tory MPs are now grovelling at Boris Johnson’s feet in a desperate attempt to further their own careers.”

It comes as Mr Johnson’s campaign aides sought to play down reports they are considering plans to prorogue Parliament in late October – a move that could prevent MPs stopping a no-deal Brexit.

The Tory leadership frontrunner’s team is said to be looking at scheduling a Queen’s speech for early November.

Parliament would be unlikely to sit for a week or two ahead of the speech, which could hamper MPs’ chances of blocking a no-deal Brexit if a deal had not been passed by that point. A source close to the campaign said the team was “discussing everything as an option”, but Mr Johnson wanted to secure a deal with Brussels and avoid a no-deal exit.

Tory former minister Guto Bebb, a prominent Remain supporter, said he believed Mr Johnson’s campaign was “quite seriously contemplating” suspending Parliament.

He said: “It would basically mean that a no-deal Brexit, which has no democratic mandate whatsoever, would be imposed upon the people of this country without this House sitting.

“And I think that would be an outrage to our democratic traditions, it would be unacceptable and the worst part is I believe they are quite seriously contemplating doing just that.”

On Monday, Mr Johnson said the problem with the controversial Irish backstop was “fundamental” and suggested he would not accept tweaks such as a time limit or a “unilateral escape hatch”.

His comments sparked a sell-off of the pound, which fell to its lowest levels against the dollar in two years. Shadow Chancellor John McDonnell said Mr Johnson’s willingness to deliver a no-deal Brexit was “playing games with people’s livelihoods”.

Tory former Attorney General Dominic Grieve accused Mr Johnson of becoming “radicalised” on Brexit and leaving the UK with “starker” prospects by trying to appease hardliners in a strengthening of his stance on the backstop.

Mr Grieve said prorogation was a “disgraceful” suggestion that would “spell the end of democracy as we know it”.

He warned whoever becomes the next prime minister that their government will collapse if they pursue a no-deal departure from the EU.

“When challenged and confronted, he radicalised even further and excluded any possibility of trying to negotiate some way out of the backstop at all. It had to go in its totality,” Mr Grieve said.

“I’ve always been willing as a politician to listen to people willing to come up with credible compromises, but what I’ve found so staggering about the Conservative leadership is it has been played to a tune of growing extremism.”

Scottish Tories ‘ready to declare loyalty’ to Boris Johnson