TOP political analyst Sir John Curtice has cautioned the SNP against putting a Plan B route to independence in its Holyrood manifesto warning it could weaken its negotiating position with Boris Johnson to get a section 30 order.

The leading academic said the party would need to present a clear position to voters before the Holyrood election about what it sought from the Prime Minister.

An inclusion of an alternative process to independence could risk such clarity and “let Johnson off the hook”, he said.

“If you want to maximise the pressure on the UK Government you don’t want to tell them what your Plan B is,” he said.

“If you want the result of the election next year to maximise the pressure on the UK Government, then you want to be able to say. ‘We went to the people, the people have said yes, so can we please have our referendum in exactly the same way we did in 2014.

“If you have said too much along the lines of if we can’t have one, we will hold one anyway, you are letting the UK Government off the hook.

“You have to make the proposition, put it to the public in an unambiguous way. We want a repeat of the process of 2014. Fullstop.”

He added: “It’s not to say the SNP shouldn’t have a Plan B, but it’s for their consumption, not for public consumption.”

Sir John, who is professor of politics at Strathclyde University, gave his views as a poll for YouGov put support for independence at 53% and forecast a record win for the SNP at next year’s Holyrood election.

The survey found some 57% of Scots were intending to vote for Nicola Sturgeon’s party, a result which would net the SNP an unprecedented majority of 74 MSPs.

The constitution is reserved to Westminster meaning the Scottish Government has to seek a transfer of powers to Holyrood to hold a legally binding referendum on independence. Such a move was granted by former Prime Minister David Cameron ahead of the 2014 vote.

But Johnson has repeatedly refused for the powers to be transferred again, saying the vote six years ago was a once in a generation event. The impasse has led to a discussion about a way forward to secure independence if Johnson continues to stick to this stance.

MP Angus MacNeil and Inverclyde councillor Chris McEleny last year tried to get the SNP to back a Plan B route. But their attempts were defeated following a stormy debate at the party’s conference in Aberdeen.

Jess Sargeant, an analyst at the Institute for Government, said Johnson could still refuse a Section 30 order if the SNP won a majority next year, but it would be politically difficult.

“From a legal and constitutional perspective, the decision of whether to grant a section 30 order is for the UK Government alone. Therefore the Prime Minister could continue to refuse to grant one, even in the event of the SNP majority in the Scottish Parliament elections.

“However, from a political perspective, an SNP victory in May 2021 – following a campaign in which indyref2 is a key issue – will strengthen the Scottish Government’s argument that there is support for a second vote amongst the Scottish public.

“This will make it harder for the UK Government to continue to make the case that the result of the first independence referendum should continue to be upheld, and the issue should not be revisited.”

She added: “An SNP majority in the 2021 Scottish Parliament elections would increase the pressure on the UK Government to grant a section 30 order, however there is no guarantee that it will do so and no clear legal mechanisms to force it to.”