Tory leadership rivals Jeremy Hunt and Michael Gove have made clear they would not facilitate “in any circumstances” a second Scottish independence referendum if they became Prime Minister.

Their declarations came as the six candidates for the Tory leadership prepare for a second TV debate on the BBC on Tuesday evening, which will include frontrunner Boris Johnson.

The live head-to-head event will take place at 8pm, just two hours after the results of the second ballot are due to be announced and which will see at least one candidate eliminated. More votes are set to follow on Wednesday and Thursday until only two candidates remain.

Mr Johnson received an early morning boost on Monday when Matt Hancock, the UK Health Secretary and one of the original 10 candidates, announced he was backing the former Foreign Secretary.

READ MORE: Boris Johnson: Stop Scottish people from becoming PM

However, Rory Stewart received some early evening cheer after David Lidington, Theresa May’s de facto deputy, rallied behind the International Development Secretary.

The Cabinet Office Minister turned up at the candidate’s latest “big tent” rally on London’s Southbank last night, telling the audience there was a “yearning in this country for political leaders who tell it straight to people” and who were honest about the difficulties ahead.

He added: "What Rory has done in his campaign is to demonstrate that there are no no-go areas in this country for him or for the party which he aspires to lead."

A source close to Mr Stewart said Mr Lidington’s endorsement was a “huge vote of confidence not just in Rory's campaign but in his ability to deliver as prime minister".

Earlier, Paul Masterton, the Tory MP for East Renfrewshire, came out for Mr Stewart, having originally backed Mr Hancock. He said his fellow Scot “really gets the Union with ideas to strengthen and secure it".

The Aid Secretary had been one of the rank outsiders before the first round vote but has now been put in second place by the bookies on the back of Sunday evening’s live debate. He polled 19 votes in the first round and needs 33 to progress through the second vote.

Mr Stewart claimed he had the necessary 33 backers to make it through the second round of voting in the contest but noted: “If they do what they say."

At a hustings before Westminster journalists, when five candidates set out their cases – Mr Johnson again failed to turn up - Mr Hunt appeared to go further in categorically ruling out a second independence referendum than when, at the weekend, he set out three conditions for facilitating such a poll.

These were: the SNP achieving a majority at Holyrood in 2021; setting a “clear timetable” for abandoning the pound and ruling out a “wildcat referendum”.

Asked if he would still deny Nicola Sturgeon another vote on Scotland’s future even if the SNP won a majority at Holyrood in 2021 but failed to meet one of the other conditions, the Foreign Secretary declared: “I am a Unionist to my core.

“I have Welsh blood and Irish blood, I spent part of my childhood in Scotland. I will never allow anything that will allow our Union to be broken up in any circumstances.”

Asked by a Lobby reporter if he had any conditions for facilitating a second independence referendum or was his position a flat refusal, Michael Gove, the Environment Secretary, replied tersely: “It’s a flat no.”

Mr Gove told the gathering of some 100 journalists that he was best placed to be the next Conservative PM as he was the candidate who “struck fear” into the heart of Jeremy Corbyn most.

Dominic Raab, the former Brexit Secretary, was questioned about the EU’s claim that he was a bad negotiator and replied: “They would say that, wouldn’t they? That’s why I am the candidate the British people can trust - whatever they say in Brussels - to get us out of the EU by the end of October.”

Later, all six candidates were grilled behind closed doors by Conservative MPs.

A source close to Sajid Javid's campaign said the Home Secretary told the Tory hustings: "I'm the best person to take on Boris. My background is different."

The campaign insider explained how Mr Javid insisted the Tories needed to do better with ethnic voters. Referring to the 2017 General Election campaign, the Secretary of State said: "If we kept our BAME vote where it was in 2015, we would have had a 28-seat majority. We need a different messenger."

READ MORE: Labour's Brexit strife breaks out after Tom Watson urges UK party to campaign for second EU vote

Amber Rudd, the Work and Pensions Secretary, who is supporting Mr Hunt said she wanted the Foreign Secretary to come second in the next round of voting, “so he can be seen going around the country and really have the opportunity to put the case".

Former Defence Secretary Gavin Williamson praised Mr Johnson's pitch, saying: "It was a commanding performance. Everyone felt very confident there was a man who had the vision, the belief, in delivering for both the party and the country."

Last night, it was suggested Mr Johnson, if he won, would instigate a review of the HS2 rail line between London and northern England.