Media playback is unsupported on your device Media caption Nicola Sturgeon says the strength of the Scottish economy will encourage people to vote in favour of independence

The Yes campaign will put a "ruthless" focus on the benefits of independence in the coming months, according to Nicola Sturgeon.

In an interview with BBC Scotland, the deputy first minister predicted the economy would be the key battleground for both sides of the debate.

And she attacked the pro-Union Better Together campaign for failing to put forward an "alternative vision".

The independence referendum will be held on 18 September.

Speaking to BBC Scotland's political editor Brian Taylor, Ms Sturgeon conceded that the Yes campaign had considerable ground to make up in the polls, but said she was "optimistic and confident" that voters would choose independence.

I firmly believe who wins the economic argument will win the referendum Nicola Sturgeon

She said that, with eight and a half months to go, the Yes campaign would focus on persuading voters that Scotland could afford to be independent, and pointing out the wider benefits of independence.

Ms Sturgeon said highlighting Better Together's "lack of alternative vision" would also be a key campaign strategy, and said the Scottish government's White Paper on independence, which was published in November, was "the only vision there is for the future of Scotland".

'Turn the debate'

Asked whether the pro-independence Yes Scotland campaign needed to be revitalised, Ms Sturgeon said: "I firmly believe who wins the economic argument will win the referendum.

"Scotland can more than afford to be independent, something that even the No campaign agrees with. We need the powers over the economy to get faster and more sustainable growth into the economy for the long term.

"There will be a ruthless focus on the benefits of independence for Scotland, from the transformation in childcare through to a reduction in APD [air passenger duty] and what we can do to get our economy growing.

"It's that message that will turn the debate and win the campaign for Yes."

Women perhaps take longer to make up their minds than men Nicola Sturgeon

Asked about polling that showed female voters were less likely to be pro-independence, Ms Sturgeon admitted that the Yes campaign had to do more to persuade women.

"Women perhaps take longer to make up their minds than men," she said.

"I accept that we are coming from behind in the opinion polls, that we require to close the gap and overtake the No campaign, but I think we've got the message, the policies and we've certainly got the determination to do that."

'Not stupid'

Ms Sturgeon also used the controversy over the future of the currency in an independent Scotland to attack Better Together.

The UK government has said it would be "highly unlikely" that it would enter into a sterling zone with an independent Scotland.

The Scottish government maintains that keeping sterling would be the best option for both Scotland and the rest of the UK.

She said: "It is not enough for the No campaign simply to shout 'no, you cannae do that'. They need to come up with more.

"They cannot continue to put forward propositions that manifestly would be against the interests of the public elsewhere in the UK, because people are not stupid and they don't believe it."

Brian Taylor's interview with Alistair Darling, who leads Better Together, will be broadcast on Friday.