The SNP is being challenged to “get off the fence” and back calls for a referendum on the terms of Brexit.

While Nicola Sturgeon has said she would not block such a vote, Scottish Liberal Democrat leader Willie Rennie is demanding her party speak up in favour of a so-called “people’s vote”.

Mr Rennie will issue the challenge as he addresses his party’s UK conference in Brighton.

He will also use his speech to stress Brexit shows “breaking up is hard to do”, insisting the reaction to Britain quitting the European Union (EU) should not be for Scotland to then leave the UK.

The UK is due to end its membership of the EU in March 2019, but Mr Rennie will say that after 40 years “the ties that bind us are strong, the economic relationship is deep”.

He will say: “Breaking up is hard to do.

“There is a lesson for Nicola Sturgeon. Rather than rubbing her hands with glee that Brexit could help her win independence, Nicola Sturgeon must surely see the obvious?

“After three hundred years the ties that bind us are strong, the the economic relationship is deep, the laws are common.”

The Scottish Liberal Democrat leader will argue: “The lessons of Brexit are the lessons for independence.

“Everyone can see it. Except Nicola Sturgeon and the SNP.

“The rest of the world can see the lesson of the destruction of a single economic market.

“They can see the harm of making it harder for business to get goods and services to market, harder for individuals to get the benefits and opportunities that brings.

“But the SNP response to the break-up of the EU single market is to break up the UK single market.

“The SNP response to the break-up of the EU customs union is to break up the UK customs union.

“I cannot for the life of me see how the SNP can conclude from all this that the response to the break up from Europe should be the break-up of Britain. Breaking up is hard to do.”

He will continue: “For those who say that we need independence to escape Brexit I tell you quite frankly that the SNP will not put automatic EU membership on their independence ballot paper.

“That’s because they care first and foremost about independence.

“After all they supported independence even when the they opposed Europe in the 1970s.

“They supported independence before North Sea oil. It always comes first.

“And now they won’t even help the rest of us get the chance to have a final say on the deal.”

Rennie will argue: “Scotland deserves better than this. Scotland demands better.

“I say to the SNP: Get off the fence. Stand up for Britain’s place in Europe. Put your voice behind a public vote on the deal.”

SNP MSP Rona Mackay hit back and said: “This is ludicrous stuff from Willie Rennie who – bizarrely – would rather attack the SNP Government over Brexit than the Tories or Labour.

“It is Theresa May and Jeremy Corbyn who both want to drag Scotland out of Europe against our will – not the SNP.

“And Willie Rennie has now made clear he too would rather that Scotland suffers the catastrophic effects of the Tories’ Brexit shambles than be a self-governing, independent country in Europe.

“With contributions like this, it is no wonder the Lib Dems are comprehensively rejected by the people of Scotland at election after election. Willie Rennie is an irrelevance, who has taken them absolutely nowhere.

“The Lib Dems should be joining our fight to keep Scotland in the Single Market – which is around eight times bigger than the UK market alone – backing jobs, living standards and our economy, and keeping the pressure on the Tories who have no mandate here.”