Boris Johnson has been dogged by questions over his character as he tried to sell himself as a defender of the Union at the Tory leadership battle’s sole hustings in Scotland.

One female activist asked him if a good prime minister also had to be “a loyal husband and father”, while another accused him of “lying on various occasions” to get out of a jam.

A rattled Mr Johnson agreed character was a legitimate issue but refused to talk about his private life, saying if people didn’t like that he would “live with it”.

The tetchy exchanges came as Mr Johnson and Jeremy Hunt fielded questions from around 500 party activists in Perth.

Mr Johnson is the strong favourite to win the race for No. 10, with a new You Gov/Times poll of Tory party members showing he is backed by 74 per cent. Mr Hunt is on 26%.

The pair were greeted by around 150 vocal pro-independence supporters outside Perth Concert Call, with banners reading “End London Rule” and “England Get Out of Scotland”.

There were chants of “Scum! Scum! Scum!” as activists entered the venue. Both candidates used the Scottish event to burnish their Unionist credentials, saying they would maintain the Barnett funding formula that determines Holyrood’s budget.

Mr Hunt was the more emphatic of the two in saying he would block a second independence referendum, even if the SNP won a majority at Holyrood at the 2021 election.

He said: “I’m a Unionist to my core. I say this: as prime minister of the United Kingdom I will never allow our Union to be broken up, and if the First Minister of Scotland asks me for a second independence referendum I will muster up my British politeness and I will say No.”

Mr Johnson said he could “see no case” for a second referendum. Mr Hunt, who this week said he was willing to work with Nicola Sturgeon on all issues bar independence, also launched a scathing attack on the SNP as “a nationalist party that is the most bullying, divisive, duplicitous, anti-business government Scotland has ever seen”.

He suggested the First Minister was slacking over preparations for a no-deal Brexit, something critics accuse of her doing in order to hasten independence. Mr Hunt added the Scottish Government had been “very disappointing” in its preparations for no deal, and he “would like to see more focus on that from Nicola Sturgeon”.

But it was Mr Johnson who dominated the event, saying he would put the Union before Brexit and claimed the latter would hurt rather than help the SNP. He said: “My first priority is obviously the Union. I think a great Brexit and a sensible, pragmatic Brexit can be a great thing to entrench and intensify the Union.”

He said Brexit would make it harder for Ms Sturgeon to sell independence and a return to EU rules, such as re-entering the Common Fisheries Policy. “I think that far from weakening the Union a good sensible Brexit will spike the guns of the SNP and strengthen the Union,” he said.

The former foreign secretary also denied being damaged by a campaign organised by senior Scottish Tories to stop him becoming leader.

But Mr Johnson also faced uncomfortable questions from activists about his morals.

He split from his second wife Marina Wheeler, with whom he has four children, last year, after a turbulent 25 years of marriage.

His subsequent relationship with Carrie Symonds threatened to derail his Tory leadership bid when police were last month called to a late-night row at their home.

One activist calling herself Flora said she was “leaning Boris” but one question gave her pause: “Does a good prime minister need to be a loyal husband and father?”

Mr Johnson said he never commented on such “stuff” before moving rapidly on to Jeremy Corbyn’s tax policies.

Asked by moderator Colin Mackay, the political editor of STV, if that helped her, Flora said: “If you choose not to comment on it you’re just going to have to let us doubtful voters come to our own conclusion, and it may not be a favourable one.”

Mr Johnson replied: “Then I’m going to have to live with it.”

When Mr Mackay said people wanted to know if Mr Johnson could be trusted as an individual, he said he had more than delivered on his promises as Mayor of London. Pressed by Mr Mackay on whether he would answer questions about his character, members of the audience jeered and shouted “move on”.

After a softer audience question, Mr Johnson was taken to task by Lochie Spearman, 67, a “third generation Conservative” from Perthshire whose father and grandfather were MPs.

After acknowledging Mr Johnson had “charisma in spades”, he asked: “Can we trust you to lead this country when you have so many times had stories about you being untrustworthy in public and private life?”

He accused Mr Johnson of “lying on various occasions” and “tending to fib” in a corner. Mr Johnson said he had been maligned in the media for promoting Brexit and putting the pledge of another £350m for the NHS on the side of a bus.

Mr Johnson also dismissed a recent YouGov poll which found most Tory voters in England were ready to sacrifice the Union in return for Brexit.

Former Tory Prime Minister Sir John Major yesterday backed Mr Hunt, telling the BBC: “I cannot vote for someone who was part of the Brexit campaign that misled the country.”

Mr Spearman told The Herald afterwards: “He’s a known fibber who never answers his questions. I fear for Scotland if he becomes leader because I don’t think he’s good for it. I just hope we don’t have him.”

Some party members leaving the hustings in Perth said what they heard had not changed their mind on their voting intentions – and did not think questions on his private life were relevant.

Terry Earp, 72, from Ardnamurchan, said he backs Mr Johnson, adding: “I haven’t changed my mind from what I thought. “Boris was best tonight, for all the bluster. I don’t think the questions that came up regarding his private life were relevant to this evening.”

The decades-long Tory member said: “I don’t think it will hurt his prospects, I think it’s already been factored in.” SNP Westminster leader Ian Blackford said Mr Hunt’s refusal to grant Indyref2 was “high-handed arrogance that may appeal to the Tory faithful but it certainly won’t appeal to the rest of Scotland”.

He said: “No wonder support for the Tories has plummeted in Scotland – and no wonder support for independence is continuing to increase.

“The mandate to hold another independence referendum is not a matter of opinion – it is a matter of fact.”