NICOLA Sturgeon’s fallback plan to fight the next general election as a ‘de facto’ referendum on independence has been challenged by Alex Salmond’s Alba party.

The UK Supreme Court is due to hear a case next month on whether Holyrood already has the power to hold Indyref2 without Westminster’s approval.

The First Minister has said that if the Court rules Holyrood cannot hold the vote legally, she will fight the next general election on the ‘single question’ of independence instead.

Both the SNP and Greens have said they will stand under their own banners and if the combined vote of the pro-independence parties standing on the same basis exceeds 50 per cent, it would be a mandate for independence.

However Mr Salmond’s party has proposed a different option, potentially muddying the waters and making it easier for unionists to discount the result if it goes against them.

Supported by Mr Salmond and the party’s national executive committee (NEC), a resolution will be debated at next month’s Alba conference in Stirling on ending the Union. 

Instead of waiting on the Supreme Court, it says there should be “an immediate and sustained campaign of parliamentary action, popular agitation and diplomatic initiative to force Westminster’s acceptance of an agreed referendum promised for October 19th 2023”.

In addition, a full case in international law should be prepared in support of Scotland’s right to self-determination.

Instead of pro-independence parties standing apart at the next election, it says they should add a “Scotland United banner” to their names on the ballot paper. 

And, crucially, instead of a majority of votes cast being the threshold for winning a “plebiscite election”, the election of a majority of pro-independence MPs “should be treated as a mandate for the Scottish Government to negotiate independence with Westminster”.

However the SNP has explicitly rejected using a majority of MPs as the benchmark for claiming such a mandate.

This is because, under the first-past-the-post system, that can be achieved with far less than half the popular vote, making it unlikely other countries would recognise it. 

The SNP won a majority of MPs in the 2015, 2017 and 2019 elections with 50, 36.9 and 45% of the vote respectively.

The UK Government has repeatedly refused to grant Indyref2, arguing the No result of 2014 was a once-in-a-generation decision.

Even if most Scots did back the SNP in the general election, the UK Government would not be obliged to interpret that in the same way as Ms Sturgeon.

An Alba party spokesperson added: “Independence and tackling the cost of living crisis will be front and centre of our discussions of conference. 

“Both matters are fundamentally related as it is an absurdity that Scotland is an energy rich land of plenty but we have Scots living in fuel poverty.”