Liam Fox has accused Nicola Sturgeon of behaving like a "political Pied Piper" who believes she can take voters with her on every issue including Europe.

The former Conservative defence secretary attacked what he described as the SNP leadership's "arrogance" as he prepared to speak at a Grassroots Out campaign event in Glasgow tonight.

His comments came as a new poll suggested that only around one in five Scots, 19 per cent, plans to vote Out, but nearly a third, 29 per cent, are still undecided.

In an interview with The Herald Dr Fox hit out at Ms Sturgeon's avowedly pro-EU campaign.

“The SNP leadership should not have the arrogance to believe that they speak for every SNP voter, all of whom will have the same weight as Nicola Sturgeon when they cast their vote," he said.

"And I think this might be an enforced lesson in humility for all the party leaders.

"They are giving voters advice, they are not some kind of political Pied Piper who is going to automatically pull the voters behind them.

"Voters are perfectly capable of making up their own minds... And I think party leaders should recognise that.”

He also suggested that many of those telling pollsters they 'don't know' how they will vote will quietly back leaving the EU.

“There is a very high number of 'don’t knows', " he said. "The question is how many of those are 'won’t says' – because they feel that they are out of step with the perceived conventional wisdom in Scotland, but could have a huge impact.”

Many SNP supporters would "will nod their heads and quietly vote for Leave,” he predicted.

He also insisted that he had a positive message to convey, saying: I don’t think of it as leaving I think is rejoining the rest of the world... where most of our future prosperity lies”.

And he defended taking part in tonight's event, which features controversial Ukip politicians David Coburn and Nigel Farage.

As well as tonight's event Grassroots Out has also announced a speaking tour of Scotland, taking in Inverness, Stornoway, Lerwick and Kirkwall, featuring former SNP deputy leader Jim Sillars and ex-Labour MP Nigel Griffiths.

Today David Cameron will launch the 'Brighter Future IN' campaign designed to encourage young people to cast their ballot in the June 23 referendum.

In supporters admit that older people are more likely to back leaving the EU and to turn out to vote.

The Prime Minister will warn the under-40s that they face being hardest hit in the event of a downturn caused by the UK pulling out of Europe.

He will also urge them to encourage older relatives to vote to stay in the EU.

“Get out there, " he will say. "Register. Vote. Tell your parents, grandparents, friends and colleagues: this referendum will really help determine whether your generation is stronger, safer and better off."

Meanwhile, union leaders claimed that workers could lose rights including to paid holidays if the UK left the EU.

Ukip has also pledged to build a "Celtic coalition", saying that Scotland, Wales and Northern Ireland should unite against illegal migration and support British jobs.

Elsewhere on the campaign trail, former foreign secretary Lord Owen said that Brexit was necessary to protect the NHS private interests if a controversial EU-US trade deal goes ahead.

Former farming minister George Eustice also claimed that 'Brexit' would cut red tape for farmers.