Boris Johnson has refused to say if he would mount a legal challenge to a second independence referendum, if Nicola Sturgeon does press ahead with another ballot without the agreement of UK ministers.

Instead, the Prime Minister highlighted the AstraZeneca coronavirus vaccine as being a prime example of the "strengths and advantages" of the United Kingdom.

His comments came after the SNP on Saturday released an 11-point "roadmap" to an independence referendum - in which it made clear a ballot could take place if May's Holyrood elections result in a pro-independence majority, even if Westminster refuses to grant a Section 30 order.

READ MORE: Michael Russell warns Boris Johnson over indyref2 court challenge

There have now been 20 consecutive polls suggesting a majority of Scots could vote in favour of independence.

And if the Holyrood elections in May result in a majority of MSPs coming from parties supporting Scotland leaving the UK, the Constitution Secretary Mike Russell said he did not believe in those circumstances Westminster would mount a legal challenge to such a vote.

He said: "I think it's such a bad look for any government to say: 'Even if the people of Scotland vote for something, we'll take them to court to stop them.'"

Johnson was pressed on the issue as he visited a coronavirus vaccine site at Barnet Football Club in North London, with the Prime Minister speaking out about the "benefits of our wonderful union".

READ MORE: Douglas Ross: Scots must boycott indyref2 if held without UK consent

The Prime Minister, who has repeatedly opposed a second independence vote, said: "The whole UK is going through a pandemic, I think what the people of the UK want to see is everybody focusing on beating that pandemic, which we are, rolling out the vaccine, and getting ready to bounce back from that pandemic and have the strongest possible economic recovery.

"I think people also can see everywhere in the UK the visible benefits of our wonderful union.

"A vaccine programme that is being rolled out by a National Health Service, a vaccine that was developed in labs in Oxford and is being administered by the British Army, so I think the strengths and advantages of the Union speak for themselves."

Meanwhile, Scottish Conservative leader Douglas Ross said Scots should boycott a second referendum if it is not held with Westminster's consent.

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Ross, speaking at an online event hosted by the Centre for Policy Studies, spoke out against the prospect of "another divisive referendum".

Speaking about the SNP, he said: "They should be fighting to protect jobs, they should be fighting to protect the businesses who are struggling to survive, rather than fighting for another divisive independence referendum, indeed even threatening to go to court for that."

He insisted it was "not inevitable" the SNP will win a majority at May's Scottish Parliament elections - despite polls showing Sturgeon's party on track for this.

Ross added: "Independence is not inevitable either, we have just got to change that narrative."

READ MORE: Scottish independence: New poll is 20th in a row to put Yes vote ahead

He insisted if the 2014 vote had been the "gold standard of referendums" then "no-one who believes in democracy should enter into this wildcat referendum that would have no actual bearing in terms of the outcome, would not be enforceable".

Ross blasted: "It is moving all the focus away from what Scottish politicians should be concentrating on right now: protecting jobs, improving the economy, supporting communities right across the country, making sure our education system is fit for our young people.

"That is where the focus should be, not on wildcat referendums, which I would absolutely boycott because they would be an absolute waste of precious time and resources when our focus should be on defeating Covid-19, rolling out the vaccine and concentrating on our economic recovery."