NICOLA Sturgeon is being urged to set a deadline of the end of March this year for Boris Johnson to agree to a second independence referendum.

The call has been made by Angus MacNeil and Chris McEleny who argue if he is still refusing to agree a vote by March 31, then the SNP and Scottish Greens should enter the Holyrood election promising a pro-independence majority will be a mandate for the Scottish Government to hold a referendum without the PM’s consent.

Their intervention comes a week after Boris Johnson indicated there shouldn’t be another vote on Scotland’s future until 2055.

“At the moment we are allowing Boris to have a veto over a referendum,” said MacNeil, the SNP MP for the Western Isles.

“By setting a deadline of March 31 for him to agree to a referendum, if he again says no, then we can contest the Scottish Parliament elections on the grounds that the only permission we will be seeking, in regards to a choice on Scotland’s future, is from the people of Scotland, not from Boris Johnson.”

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McEleny, who along with MacNeil, has been the most vocal advocates of a Plan B route to independence, wants the Scottish Government to drop its current position that a referendum should happen only via the route taken ahead of the 2014 vote, of the UK Government agreeing to a transfer of powers to Holyrood under a section 30 order.

“In the event that the UK Government do not meet the deadline set by the Scottish Government, pro-independence parties must enter the Holyrood elections clearly setting out that in the event of a pro-independence majority of MSPs being elected to the Scottish Parliament then this will be a mandate for the Scottish Government to hold a referendum on Scottish independence,” said McEleny, who leads the SNP group on Inverclyde Council.

“Safe in the knowledge that the UK Government will not support the referendum, the Scottish People will give popular legitimacy to their parliament legislating for a referendum by electing a pro-independence majority of MSPs.”

The First Minister has said she wants a new referendum “in the earlier part” of the next Holyrood parliamentary term, which runs between 2021 and 2026.

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Senior SNP figures including Ian Blackford (above) and Michael Russell have also backed a second referendum this year.

The First Minister has described the route taken to hold the 2014 plebiscite as “the gold standard” and has been reluctant to back an alternative course.

Earlier this month, she reiterated her Government’s commitment to a “legal, constitutional rule to becoming an independent state”.

However, amid the Prime Minister’s continuing refusal to agree to a new Section 30 order, she has come under internal pressure from senior figures and the SNP ‘s grassroots to consider other options.

Writing in The National last week, SNP MP Joanna Cherry welcomed a discussion, to take place at the party’s National Assembly later this month, saying while a majority vote in a referendum was the best way to achieve independence, there were also alternative options.

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She wrote: “On January 24, an SNP virtual National Assembly will take place to discuss ‘the tactics and strategy on the route from here to Independence Day’.

“SNP depute leader Keith Brown is to be commended for securing this important discussion which is open to all party members and will be conducted in private.

“A recent opinion poll suggested two-thirds of voters want a fall-back strategy to secure a second independence vote if a Section 30 order is refused this time round.”

SNP MP Kenny MacAskill has also cast doubt on the Prime Minister agreeing to a second independence referendum.

Along with MacNeil, the former justice secretary, who now represents East Lothian at Westminster, signed affidavits formally supporting a landmark court case aiming to prove that Scotland does not need permission from Westminster to hold a second independence referendum.

READ MORE: Michael Russell: We won’t just have Plan B – we’ll have Plan A to Z to get indyref2

Shortly after he was elected as SNP president in November last year, Russell insisted the Scottish Government would not only have a Plan B to secure independence, but a “Plan A to Z”. Some 17 successive polls have given independence majority support.

"If the people of Scotland vote for something they must have it. The role of the SNP is if they vote for the SNP to deliver it, then the SNP must deliver it." he told the Sunday National in an exclusive interview.

“So therefore we will find a way to deliver it and I think we just don’t need Plan B, we need Plan A to Z and we have lots of ideas to do with that.”

Later this month the SNP will hold a national assembly to discuss alternative routes to independence in the absence of an agreement from the Prime Minister for a new vote.