Responding to Chancellor George Osborne and other No campaign leaders, who last week dismissed the SNP's plan for a sterling currency union, Swinney says it is "blindingly obvious" the pound is Scotland's currency every bit as much as it is England, Wales and Northern Ireland's, and that would not alter with a Yes vote.
Any UK government that denied Scotland a currency union would be "cutting off its nose to spite its face", Swinney writes in the Sunday Herald, given the positive impact North Sea oil has on the UK's balance of payments, which strengthens the pound.
But Liberal Democrat Chief Secretary to the Treasury Danny Alexander, also writing in the Sunday Herald today, calls Swinney's position "glib". He argues the SNP has failed to address the difficulties of currency union identified in a new Treasury analysis last week.
"It won't do for the SNP to invent arguments, twist facts or conjure numbers out of thin air," Alexander said.
The pro-union Better Together campaign last night released a YouGov poll it commissioned which found almost two-thirds of Scots think Alex Salmond and the SNP have failed to make a convincing case for independence.
The economy, pensions, the currency, the NHS and tax emerged as key voter concerns in the poll, which surveyed 1038 adults between 24 and 26 April.
But although it found the currency was important in how Scots will vote on September 18 next year, it was not as important as the Unionist side might have hoped.
Only 19% said swapping the pound for the euro or a new currency would make them less likely to vote Yes, as most had already made up their mind: 44% said they would vote No regardless of the currency and 23% said they would vote Yes regardless.
The economy was picked by 59% of those asked for their top three deciding factors, against 39% for tax and spending levels, 36% for welfare and pensions, 30% for health services, and 22% for the currency.
Only 30% of those asked felt the Nationalists had made a fairly or very convincing case for leaving the UK, while 62% thought it was fairly or very unconvincing. Some 37% of those questioned believed the Yes case so far was "not convincing at all".
Scepticism about independence was closely linked to party allegiance: 98% of Tories, 91% of LibDems and 82% of Labour voters are unconvinced by SNP arguments. But even 24% of SNP voters felt their party hadn't done enough to make its case.
SNP campaign director Angus Robertson MP said: "All this poll proves is that the No campaign is being led by what the Tory government says – a fact which will haunt their campaign."
Questions over the currency arrangement for an independent Scotland dominated the political agenda last week after a Treasury analysis questioned Alex Salmond's assumption that the UK would readily agree to share the pound.
The First Minister's plan for a sterling currency union was scorned by the Chancellor on a visit to Glasgow.
Osborne said it was unlikely the arrangement would be made to work, given the difficulties of the eurozone currency union. However, he failed to rule out such a union after a Yes vote, a point seized on by the SNP as evidence that his argument owed more to low politics than economics.
The focus on currency coincides with campaign offensives by both sides in the independence debate, with a surge in canvassing after the winter lull.
While Yes Scotland will push the message that an independent Scotland could be one of the most prosperous nations on Earth, thanks to £1.5 trillion of oil reserves, Better Together is distributing a million leaflets saying: "The only way to keep the pound is to vote to stay in the UK."
In a newspaper interview yesterday, former RBS chairman Sir George Mathewson said Osborne's "fear tactics" were weak and ineffective. Mathewson said: "This kind of tactic will not work. To have one more snooty English person coming up and telling us how things are going to be - in most parts of Scotland, it won't be all that meaningful."
LibDem Scottish Secretary Michael Moore said after floating one currency option after another the SNP was scrabbling for "Plan D". He said when the "stress-test" was applied to the party's big ideas they fell apart.
"Plan A was a separate new currency. Plan B was the euro, and Plan C was unilaterally declaring a euro-style currency zone with the UK. But the analysis we have published this week shows why it is highly unlikely that a currency zone could be agreed and made to work. So the question must be answered: what's Plan D?"
A spokesman for Deputy First Minister Nicola Sturgeon said the Scottish Government's Fiscal Commission Working Group has concluded sharing the pound is the "common-sense position".
"The Secretary of State's latest intervention is bluff and bluster. The fact that despite all their rhetoric, the UK Government haven't actually said no to a sterling zone only shows that they too know it makes sense."