TOMMY Sheppard has argued the SNP made a fundamental error in their General Election strategy by insisting the campaign was not about independence. In a rare criticism of the leadership by a senior politician in the party, the MP claimed the downplaying of the SNP’s core objective led Yes voters to switch to Labour.

Jeremy Corbyn was able to portray Labour as the engine for social change and talk of people power in a manner not dissimilar to the Yes campaign of 2014,” Sheppard said.

READ MORE: Transcript of Tommy Sheppard's landmark lecture on how we win the next referendum and what the SNP got wrong

“For some, particularly young left-leaning voters in urban areas the attraction was undeniable. I know several people who told me they voted Yes in 2014, and for me in 2015, but this time they voted Labour because they wanted to endorse, and I guess, associate with the message he was putting out.

“And, of course, given the SNP spent most of the campaign saying the election was not about independence anyway then from their point of view what’s the harm in lending their vote to Jeremy.”

Sheppard’s comments were made in the annual Thomas Muir lecture, delivered in Edinburgh on Thursday night and published in full today by The National. He identified factors which led to his party losing 21 seats in the June 8 election and put forward ways to rebuild support.

He said: “Some 480,000 people who voted SNP two years ago declined to do so this time. In 2015, the SNP had more than 50 per cent of the vote in 35 of the 59 seats – now that figure is none. This was, by any measure, a political setback for the SNP.”

Sheppard added that to win back voters who had switched to Labour, the SNP needed to underline their uniqueness as the party of independence and to link that ambition to that of bringing about social change.

On timing of a new referendum, Sheppard said he would opt for obtaining “a new, clear and unconditional” mandate at the 2021 Holyrood election ahead of one “linked intrinsically to Brexit”. He said: “This scares some in the Yes movement who fear pro-independence parties may lose a majority in the 2021 parliament and the chance of a further referendum may disappear. To them I say: have confidence in your conviction.

“There is no reason why we cannot take support for independence to far greater levels than hitherto in the next four years. Besides, if there are not the numbers to elect an independence-supporting Scottish government, then there ain’t the numbers to win a referendum in any event.

“Realistically I think those who seek independence need a plan which works backwards from 2021 ... we need a new case for independence which builds on the old. A case which answers questions left unanswered last time and takes account of changes in the world since.”