An SNP veteran has warned that plans by a controversial blogger for a new political party to contest the Holyrood elections could end up splitting the pro-independence vote.

Jim Sillars, the former depute leader of the SNP, said that a suggestion by Wings over Scotland author Stuart Campbell for another party to stand on the List could make it harder to win a pro-independence majority in 2021.

However, he said: “This is a sign of frustration on the part of people in the independence movement, which I fully understand.”

The 2021 Holyrood election is shaping up to be a single issue poll on whether the SNP and Greens can secure a majority of seats for another independence referendum.

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The two parties won 69 seats at the last Holyrood election, but the UK Government has consistently rejected another plebiscite in the current term.

Holyrood’s electoral system means that a party which performs well in the first past the post (FPTP) seats will find it harder to make gains on the eight regional Lists. In 2016, the SNP won 59 FPTP seats, but only secured four List members.

Bath-based Campbell, whose Wings over Scotland describes itself as a "Scottish political media digest and monitor", has been criticised for his attacks on opponents of independence.

He also lost a defamation case to former Scottish Labour leader Kezia Dugdale, who had accused him of sending "homophobic tweets".

It was reported yesterday that Campbell has been discussing an idea for a new pro-independence party, which would contest the 2021 election.

He said: “It’s conceivable that a Wings party might be able to pick up list seats that the pro-indy side otherwise might not."

The plan could be pushed ahead with “if it looked like there wasn’t going to be a pro-independence majority, which I think is a very real danger”.

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One senior SNP source said that such a party could, if the SNP focused solely on FPTP, win around 20 List seats, thus securing a pro-independence majority.

However Sillars, who is one of his party’s most famous figures, said: “If you set up a party that seeks to take votes away from the SNP, which presumably they are trying to do, then you make it harder to get the overall majority at Holyrood.”

He added that, far from the SNP repeating its success in FPTP constituencies, Nicola Sturgeon’s party could lose some of these seats in 2021 and need List pick-ups: “Perhaps nobody has thought that the SNP might need more people from the List than last time. You might fall between two stools. A bit of patience is required in the independence movement. What’s two or three or four years in the life of the nation?”

He warned: “I think it possibly could split the vote. It could end up a mess.”

Sillars is a critic of the SNP leadership, but noted: “We have one instrument, the SNP, and the fact of the matter is that that is the instrument we need to get independence.”

The Wings over Scotland blog stated yesterday: "As we’ve said, it’s only a half-formed thought at the moment. We’ve sounded out a few people for opinions and feelings, and in some cases asked them if they might in principle consider running for it, but that’s as far as it’s gone."