THE SNP’s independence plans have become “more extreme” since the referendum of 2014, Gordon Brown has said.

The former Labour Prime Minister, who recently launched the pro-Union Our Scottish Future project, also said the SNP was driven by divisive “us versus them” nationalism rather than positive patriotism.

He admitted Boris Johnson was “holding back” the Unionist cause, but that it would be wrong to found a case for leaving the UK on one person or their actions.

Mr Brown was speaking this morning at the Edinburgh International Book Festival, where he was in conversation with the journalist and broadcaster Jonathan Freedland. 

Promoting his latest book, Seven Ways to Change the World, a plea for more cooperation between nations, Mr Brown was asked how he could advocate stronger partnerships around the world when cooperation between the home nations appeared to getting weaker. 

He said: “If you need more cooperation, it will not do us any good, even if we've left one union [Europe, as a result of Brexit], to leave the other one.

“What's happened since 2014 - and I don't think it’s quite got through - the Scottish National Party policy in 2014 was for a form of independence that didn't involve a separate currency, and didn't involve them leaving the British customs union and the single market. 

“So the SNP in 2014 reassured people they would keep the currency, and they would stay in the British common market, the British single market, and therefore [on] trade there will be no need for a border. That is not their policy now. 

“So we've now got a more extreme policy for a separate pound, for being in outside the single market and customs union. 

“Inevitably there would be a border between Scotland and England. It’s unavoidable in these circumstances.

“And we’d put at risk the jobs and the trade that happened, because we trade with England more than we trade with any country in Europe, about 10 times more so at the moment.”

Under the SNP’s plans, Scotland would rejoin the EU after independence, so the border with post-Brexit England would also be a tightly regulated external EU border.

During the Holyrood election campaign, Nicola Sturgeon admitted this would create a physical border and raise “all sorts of issues” and “practical difficulties” for trade.

She said she would work to make trade with a post-Brexit UK and with the EU as smooth as possible, but has yet to set out any plans for doing so.

Mr Brown went on: “The argument, it seems to me, for cooperation is greater. 

“You can't solve climate change just in Scotland. You can't deal with a nuclear proliferation threat if you're only one nation. You've got to work with other nations. 

“The basic proposition of the Scottish National Party is that Scotland and England have moved apart, that we don't have much in common anymore, that you can't be Scottish and British at the same time, and I just don't think that works.

“I just don't think that makes sense of a modern world where your independence would always be modified or qualified or constrained by the interdependence and our dependence on each other. So in a way since 2014 The argument for cooperation is stronger.

“Now, you can, you can change the constitution, you can make it different, you can make it more flexible, you can make it more adaptable.”

Mr Brown also discussed George Orwell’s distinction between patriotism and nationalism.

Orwell said the former was a positive love of country that did not require any hostility to others, whereas nationalism was antagonistic and divisive.

Asked if the campaign for Scottish independence was driven by nationalism or patriotism, he said: “It’s driven in the end by nationalism, there's no doubt about it. Because it is the Scottish National Party, and they have a nationalist agenda for a separate state. 

“The Scottish National Party when it started [in 1934], a lot of the members were in favour of a federal arrangement, they used to call it home rule, and it's only in the last 20 or 30 years that this harder view of separation, of independence, has become become the common currency.

“Nationalism is about that ‘us versus them’, it's seeing the world divided into two, between us and them. That is a nationalist ideology. That is what nationalism is about. 

“And so often we hear, it's England or London or Boris Johnson or someone who's holding us back, and I don't disagree that Boris Johnson is holding us back. 

“But you don't build your whole philosophy around one person, and what he's doing at any particular point in time. 

“So it's this us versus them ideology that is rampant in the world, of course, and I'm afraid it defines the relationship between Scotland and the rest of the UK at the moment that's got to change.”

SNP MSP Keith Brown, the party's depute leader, said: “As usual Gordon Brown wants to keep Scotland shackled to Westminster no matter the harm it causes to the people who live here.

“It is Labour and the Tories who have put up borders and placed jobs at risk by backing a hard Brexit, which saw the end of freedom of movement and access to the world’s largest trading bloc.  

“Support for independence has been driven by the desire to choose a different path than the one Westminster is currently taking Scotland down. 

“Scotland was told in 2014 that if we remained part of the UK we would remain part of the EU. And despite voting to remain in the EU in 2016, we were dragged out anyway.

“On top of this we have made it clear that we want fairer social security and migration systems based on dignity and respect. We have begun to build the former, but while the majority of welfare powers, as well as employment and migration powers remain reserved to Westminster, the Scottish Government is trying to create a fairer society with one hand tied behind its back.

“It is clear that Westminster does not work for Scotland. The only way we can secure a strong and equal recovery for the people of Scotland is with the full powers of independence and the ability to choose our own future.”