The campaign to win over the hearts and minds of the Scottish voters has begun in earnest after the signing of a deal on the independence referendum.
The opinion polls continue to fluctuate but generally show one third in favour of independence, one third in favour of the status quo, and another third who support further devolution short of independence.
However, the devo-max option will not appear on the ballot paper and it remains to be seen if the Unionist parties will attempt to turn a ‘No’ vote into ‘No…but’, promising voters more powers for Holyrood if they vote against independence.
Professor John Curtice of Strathclyde University explained the thinking to Scotland Tonight.
He said: "Mr Salmond will undoubtedly now want to say to that group: Your option isn't on the ballot paper -- can you really trust the unionist parties to deliver on this?"
During his visit to Scotland on Monday, Mr Cameron spoke to workers at the Rosyth dockyard, underscoring the issue of defence, which has proved thorny for the pro-independence side.
Professor Curtice said: "You start asking people what a Scottish Parliament should be responsible for and the point at which they chill is when you start talking about a Scottish army, a Scottish defence force. They certainly have to be persuaded that it's a good idea.
“I'm not sure arguments that Scotland would be undefended would necessarily have that much resonance, however, given that we are talking about a part of Western Europe where serious conflict is not on the horizon.”
Blair Jenkins, chief executive of the Yes Scotland campaign, appeared on Scotland Tonight and conceded that defence could play a role in voters' decision. He stressed that, although he is not a member of the SNP and does not speak for the party, he supports an independent Scotland remaining in Nato.
The party leadership is pushing for a change in the SNP constitution to overturn their long-standing opposition to the nuclear-armed common defence alliance in the hopes it might allay any concerns held by floating voters about the security of an independent Scotland.
As ever in politics, however, voters follow their pocketbooks and both sides are exchanging figures on how much better off Scots will be if their respective campaign succeeds.
On Monday, Alex Salmond suggested Scots would be £500 per year better off if Scotland becomes independent.
Professor Curtice added: "Ask people, would you support or oppose independence if you felt that everybody would be £500 a year worse off, only 21% thought they'd vote for independence. However, if you tell them they would be £500 better off, 65% said they'd support the idea.”
More About Scotland Tonight
- Sturgeon's debate message to Miliband: 'We can deliver real change'
- Labour and SNP deal would mean 'coalition chaos', says Cameron
- Coburn faces questions over Ukip's £5.5bn Scots budget cut plan
- New show from Mark Thomas tells of BAE spy in campaign group
- Patrick Harvie: Fiscal autonomy 'needs a great deal further work'
- SNP set to wipe out Labour as they widen poll gap after STV debate
- Miliband slams 'deceit and lies' of Tories over SNP Trident claim
- Lord Forsyth: Alex Salmond ‘deciding rules of game’ on referendum
- Johann Lamont: Referendum must not ‘distract from real problems’
- Alex Salmond touts ‘prosperous and successful’ independent Scotland
- Secretary of State: Voters focussed on Scotland's 'place in world'
- David Cameron promises to fight for Union in referendum campaign
- Agreement on referendum on independence between Cameron and Salmond
- Deal struck between Cameron and Salmond for independence referendum
- Scottish Lib Dem leader pledges to support more powers for Holyrood