Alex Salmond will today accuse George Osborne of a "monumental error" in ruling out currency union with an independent Scotland, even as a new poll showed a drop in support for the 'yes' camp.
An Ipsos Mori poll for STV suggested Osborne's gambit had pushed undecided voters towards voting 'no' - a key factor in the latter stages of the referendum battle.
The survey found 34% of undecided voters are now more likely to oppose independence, against 16% who said they were more likely to back independence.
Forty-four per cent of undecided voters said their position had no changed.
Support for the union remained unchanged at 57%, but support for independence fell two points since December on 32%.
Analysts hasve long said that the key to winning the September poll lies in convincing undecided voters.
The early signs are that Osborne's gambit may have influence moderate undecided voters, who are more concerned about the impact of independence on their wallet than they are by colourful rhetoric around the union or independence.
The poll was conducted between one and two weeks after the Osboprne speech, but before Standard Life announced it was drawing up contingency plans to move south of the border in the event of independence.
Meanwhile, Salmond wil be making the New Statesman lecture in London today, where he will say Osborne's move reflected all that was wrong with Westminster's relationship with Scotland.
"I believe George Osborne’s speech on sterling three weeks ago – his 'sermon on the pound' – will come to be seen as a monumental error," he will say.
"It encapsulates the diktats from on high which are not the strength of the Westminster elite, but rather their fundamental weakness."