A SECOND independence referendum will be held shortly after the next-but-one Holyrood election in 2021, the former leader of the Yes Scotland campaign has predicted.

Blair Jenkins said it was "highly likely" that a re-run of last year's poll would be held, and that Scots would vote to leave the UK.

Speaking a few days out from the anniversary of the historic plebiscite, the former television executive said the "groundwork" for another pro-independence drive had been done and voters should be asked the same Yes/No question.

He also defended the SNP's key proposal for a currency union with the rest of the UK but said he expected First Minister Nicola Sturgeon would assess other options before a second referendum.

Mr Jenkins, a former head of news at BBC Scotland, was appointed leader of the official Yes Scotland campaign in 2012 when support for independence stood at 27 per cent.

The campaign, which augmented the Scottish Government's effort by building a huge pro-independence grassroots movement, helped secure a 45 per cent share of the vote in the referendum.

Since then support for independence has climbed further, with two recent polls showing a majority of Scots in favour of leaving the UK.

In an interview with The Herald, Mr Jenkins said: "I avoid the word inevitable, which I know some people have used about a second referendum.

"But I do think it's highly likely there will be a second referendum and I think it is highly likely Yes will win."

Though "reluctant" to predict the timing, he said: "If I was guessing, I'd say 2021, round about there.

"There would not need to be nearly as long a campaign next time, so the referendum could happen fairly quickly if it were in a winning SNP manifesto.

"It could happen in a much shorter timeframe given all the groundwork has been done this last time."

He said First Minister Nicola Sturgeon should aim to "protect" Scotland's place in the EU by promising a referendum if the rest of the UK votes to leave in the referendum now expected next autumn.

However, he said he expected the UK to stay in the EU, making a second independence referendum "more likely" after 2021.

He said the number of people declaring support for independence last year had been "transformational" in sustaining support following defeat on September 18 and insisted a second campaign would start with support for a Yes vote on "at least" 45 per cent.

"The movement for Scottish independence is stronger now than it has ever been," he said.

Mr Jenkins, 58, said he would be willing to contribute to a second campaign though in a different role.

He said a second referendum should use the same question as last year, despite the Electoral Commission ruling out a Yes/No question for the forthcoming EU vote on the grounds it could be seen as unfair to the No side.

Mr Jenkins said being on the Yes side was "hugely important" to his campaign but claimed it was harder to frame the EU debate as a Yes/No question.

He added: "I do not think the question will be opened up for discussion again."

Mr Jenkins - who has not joined the SNP - defended the party's plan to share the pound in a formal currency union with the rest of the UK.

The proposal, which was ruled out by the UK Government, was criticised by some on the cross-party Yes Scotland board, who argued it would not have given Scotland sufficient autonomy and simply allowed the No campaign to create uncertainty in voters' minds about the currency that would be used in the event of a Yes vote.

Jim Sillars, the former SNP deputy leader, has described it as a "gift" to the No side.

But Mr Jenkins said concerns about currency had not prevented support for independence from rising.

He said the question of an independent Scotland's currency had been "slightly difficult terrain for everyone" in the Yes campaign but added: "That is a different thing from saying, was there a different position or option that would have secured a higher Yes vote?

"I'm pretty certain the answer to that is no."