THE SNP’s Westminster leader has said a new independence referendum “has to happen" next year as he appealed to rebels not to disrupt this weekend’s party conference over the issue.

Ian Blackford, who gives the main speech in Aberdeen on Sunday, told the Politico website the party was ready for Indyref2 despite doubts among senior members.

However he said the exact date had to remain a mystery.

Nicola Sturgeon has said she wants another vote in the second half of next year, but has not secured the required powers from Westminster to make it happen.

Nor has she explained if she has a Plan B if the UK Government simply refuses.

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Mr Blackford said: “It has to happen within 2020. What we don’t want to do at the moment is put a specific date on that.”

However, the lack of detail, and the expectation that the UK Government will continue to block a vote has prompted some in the party to demand an alternative route.

Western Isles MP Angus Brendan MacNeil and National Executive Committee member Chris McEleny have proposed their own Plan B - taking an SNP win in a Westminster or Scottish election as a mandate to start negotiating independence.

According to The National, the pair may try to use a technical device at the start of the conference on Sunday to oppose the agenda unless their idea is debated.

The First Minister repeated her opposition to the idea this week, saying there was no “shortcut” to independence via a Catalan-style wildcat referendum or other mechanism.

She said her party had to “demonstrate majority support for independence in a process that is legal and legitimate”, both in UK law and in the eyes of the EU and the world.

She said: “The SNP could, and has, won a majority of seats in a Westminster [election] on a minority of votes.

“If I wanted to try and argue we wanted to become independent on that basis, nobody in Europe would listen to me in terms of the legitimacy of that.”

Mr Blackford added: “My simple message would be that we have the mechanism which is there for us to get a referendum. So what I would say to everyone is let’s get behind the program that we have got and let’s make sure that we have that referendum.”

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Suggesting the SNP’s price for supporting a Labour government would be Indyref2, he added: “I would say to every possible candidate for PM they have to respect the mandate that we already have, and the Scottish people will be sending SNP MPs back to Westminster to make sure that mandate is delivered upon.

“That for us under any circumstances is non-negotiable.”

Mr Blackford's insistence on a vote next year could also be a sign of nerves that the SNP and Greens may lose their combined pro-independence majority at the 2021 Holyrood election, making Indyref2 impossible.

Pamela Nash, chief executive of the anti-independence group Scotland in Union, said: “The very last thing that Scotland needs is a divisive and unwanted second independence referendum next year.

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“The Brexit turmoil is causing deep divisions and economic uncertainty, and a referendum on leaving the UK would cause catastrophic upheaval.

“Nationalist politicians need to start listening to the people of Scotland. Barely a quarter back another referendum before 2021, and support for remaining in the UK has risen to 59 per cent. Scotland said no to separation in 2014 and we meant it.

“The best future for Scotland is as part of the UK, growing our economy, ending constitutional division, and investing in public services for the most vulnerable in society.”