Scottish Tory MPs will make a "pledge of loyalty" in a private meeting with Boris Johnson today, in exchange for a commitment to take their advice on decisions affecting Scotland and the Union.

The SNP has branded the move the "ultimate humiliation for Ruth Davidson" after months of speculation about the rift between the Scottish Tory leader and Johnson.

READ MORE: Scottish Conservatives set to back Boris Johnson for PM

The Scottish group of MPs will assure Johnson that he will have their support if becomes Tory leader, according to the Scotsman.

But the group 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 told the paper. “The key thing is that he listens.”

Referring to controversies over 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 Johnson’s Cabinet, will be at the meeting.

At the Tory party conference last October, Mundell said Johnson was not “an asset” to the party and accused his former Cabinet colleague of trying to create “a maximum amount of distraction and headlines for himself”.

A few months later he suggested he could not serve in Johnson's Cabinet.

But in May Mundell appeared to have changed his mind, accusing the SNP of demonising Johnson.

READ MORE: Poll reveals just how few Scots trust Boris Johnson as next PM

In total, at least nine MPs are expected to attend the meeting, compared with just five who went to an earlier meeting with Johnson's Tory leadership rival, Jeremy Hunt.

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.

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 described the Scottish Tory MPs' move as “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,” 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.”

Last year Scottish members of the party were at the heart of a campaign, nicknamed “Operation Arse”, to prevent the former foreign secretary becoming party leader. At the time, private polling indicated Johnson had abysmal approval ratings in Scotland.

Some senior Scottish Tories remain of the view that Johnson as prime minister would be “a gift to the SNP” and potentially the midwife of independence, with many liberal voters switching to the “Yes” side.

It comes as 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.