Nicola Sturgeon is seeking an urgent meeting with David Cameron to resolve the protracted funding row over the powers promised to Scotland ahead of the independence referendum.
Scotland’s First Minister has written to the Prime Minister suggesting they meet in London upon his return from European Council talks which conclude on Friday.
The Scottish Parliament’s initial deadline of February 12 has lapsed and Ms Sturgeon said an agreement must be reached by the end of this week to give Holyrood enough time to scrutinise the fiscal framework for the Scotland Bill.
She said failure to meet this deadline would lead her to conclude that the Prime Minister has failed to honour his “vow” of more powers on the eve of the referendum in 2014.
The UK Government’s head negotiator in the talks, Chief Secretary to the Treasury Greg Hands, angered Ms Sturgeon by going on holiday this week.
He rejected the Scottish Government’s latest funding proposal by telephone in a conversation with Deputy First Minister John Swinney on Tuesday.
Mr Hands has offered to return from his holiday if the Scottish Government “is willing to make a substantial move” in the negotiations.
Scottish Conservative leader Ruth Davidson has insisted the Scottish Government has not moved “even a fraction of the distance the UK Government has to reach agreement”.
But in her letter to Mr Cameron, Ms Sturgeon said “it is the Treasury, not the Scottish Government, that now needs to signal movement” – which she said must be swift and significant.
She said the deadlock has left her “no option” but to seek Mr Cameron’s intervention.
The Scottish Government says the Treasury’s latest proposal would leave Scotland £3 billion worse off in 10 years, in contravention of the Smith Agreement that devolution should cause no detriment.
But the UK Government says an unfair adjustment could leave taxpayers in the rest of the UK worse off.
Ms Sturgeon said Mr Hands’s continued reluctance to accept the Scottish Government’s proposal “makes it hard to avoid the conclusion that (the UK) Government is unwilling to agree the principle of no detriment”.
She added: “If that were the case it would mean, in my view, that you had failed to honour both your pre-referendum vow and your commitment to implement in full the recommendations of the Smith Commission.
“I think that view would be widely shared in Scotland.”
She went on: “I remain committed to reaching an agreement. However, if we are to do so we must make substantial progress – and see significant movement from the Treasury – in a short space of time.
“I hope you will be prepared to intervene to make sure that this happens.
“The Deputy First Minister remains available to travel to London at any time this week.
“If it will help to bring matters to a conclusion, I would also be willing to meet with you in London on your return from the European Council.”
Writing in The Scottish Sun, Ms Davidson suggested the Scottish Government may be considering walking away from a deal to stoke “grievance” with Westminster and appease nationalist SNP voters.
She has put forward “a compromise” to monitor how the opposing estimates play out in cash terms and review the framework in a few years to make any necessary adjustments.
“That way we can check how the formula has worked while, at the moment, the dispute centres over a guess at how it might work in the future,” she said.
She added: “The question for the SNP therefore is this: Do you want to do a deal or don’t you? There are two paths for them.
“Either they grab new powers for Scotland, with a funding formula that works and an insurance policy to underwrite it.
“Or they back a grievance agenda because they think it’s a vote winner over the next few weeks ahead of the Holyrood election.”