Scottish independence: Alistair Darling warns against referendum complacency
The result of this year's referendum will be closer than opinion polls suggest, according to Alistair Darling.
Warning against complacency, the leader of the pro-Union Better together campaign said a high turnout was essential for a "decisive result".
In an interview with BBC Scotland, Mr Darling said economic arguments would be fundamental to voters, especially those still undecided.
The independence referendum takes place on 18 September.
Speaking to BBC Scotland's political editor Brian Taylor, Mr Darling said Better Together had a "positive" case to make and persuading undecided voters would be a key tactic in the remaining eight and a half months of the campaign.
"It's important this year to try and persuade those people who are still undecided - and there are a lot of them - that we are better and stronger together," said Mr Darling.
"There's a strong positive case to be made for the United Kingdom, we have the best of both worlds with the Scottish Parliament, but we are also part of something larger. It's good for businesses, it's good for our security.
"At the same time, we've got to persuade those people who are already convinced of our argument they cannot be complacent.
"I think this is going to be a lot closer than people think and this is something where we really do need a high turnout so that we get a decisive result."
Asked whether Better Together would offer voters in Scotland more powers as an alternative to independence, Mr Darling argued the issue was "secondary" to economic arguments such as the currency.
He added that the three political parties in Better Together - Labour, the Conservatives and the Liberal Democrats - were "working towards" constitutional plans, but did not confirm that there would be a "single offer" from the No campaign to voters.
He said: "Whether or not they have an agreement, or whether they work towards that [a single offer], in some ways I think that is secondary ... the decision will be made fundamentally on the economic arguments, on what currency we're going to have, are we going to get into the European Union?, are we going to be worse off or better off?
"Of course constitutional matters and reform matter, but I think if you look at all the evidence we've seen so far, it's those fundamental economic arguments that will clinch it, especially amongst the undecideds."
Asked about reports that senior UK Tories had referred to his leadership of the campaign as "comatose" and "useless", Mr Darling said: "Frankly, in 10 years, 50 years, does it really matter?
"The big issue, and this is the single biggest issue those of us in Scotland will take probably in our lifetime, is whether or not we get the best of both worlds remaining part of the United Kingdom ... or do we take a leap into the unknown?"