The SNP's plans for Scotland to raising and spending all of its own cash finally reared its head last night in a leaders' debate, as Jim Murphy dug in his heels and pushed for answers from Nicola Sturgeon on the issue.

 

The policy had failed to come up in Tuesday night's STV programme, but surfaced in the BBC show - when the debating panel was expanded to include the Green Party's Patrick Harvie and UKIP's David Coburn.

The other subject that was widely expected to be discussed was the continuing controversy over last weekend's leaked inaccurate memo about the Nicola Sturgeon's private meeting with the French Ambassador.

The latter was absent again last night. But there is little doubt that the pivotal moment came when then the proposition of full fiscal autonomy was discussed.

Labour, seeing the issue as the major weakness in the SNP's election campaign, had planned to finally pin the First Minister down on the issue, having failed to get a straight answer at First Minister's Questions over when SNP MPs would seek to implement it. Jim Murphy got it to stick at the University's Elphinstone Hall last night, with Ms Sturgeon's answer likely to shape the debate in the weeks ahead.

Prior to that, there had been little to choose between Mr Murphy and Nicola Sturgeon on their rhetoric over economic policy. "You don't have to cut your way out of austerity. There is another way," argued the Labour leader. "It's time for an alternative," said the SNP leader.

Shortly afterwards, David Coburn made his first gaffe, a slip of the tongue seeing him describe those on low incomes as "the lowest people in society." It drew the opening First Ministerial incredulous sideways glance of the night. Groans from the audience followed in response to Mr Coburn saying he wanted "wean Scotland off" the "finished" Barnett Formula. His five opponents lined to have their turn on the UKIP punch bag. He was happy to provide the ammunition, later saying the UK should stop "squandering" cash on foreign aid.

Willie Rennie turned his sights on Ruth Davidson, perhaps taking a leaf out of Nick Clegg's book. "She is not proposing one new tax on wealthy people," he said, accusing her of attempting to "balance the books on the back of the poor". It was shaping up to be a better night for the Liberal Democrat leader.

So far, so predictable. But just after 20 minutes in, as James Cook honed in on the issue of full fiscal autonomy, the debate turned. As the BBC man pushed the First Minister on when she would like fiscal autonomy for Holyrood, Mr Murphy smelled blood. "Would your MPs vote for it next year?" he asked, putting a question that had repeatedly been dodged six days earlier. "I would vote for it, would you support it?" came the reply. Game on.

The statement, following weeks of the SNP dancing on the head of a pin over its call for devo-max in the face of a plummeting oil price, saw the First Minister replace Mr Coburn in the primary line of fire.

"After the difficult time that Aberdeen has been through, the idea that we give up voluntarily to pooling and sharing of resources, the ability to transfer money around these islands... I don't think it makes sense," said Murphy, drawing attention to the fact that the oil capital of Europe perhaps wasn't the ideal place to make this commitment. There would have been "absolute chaos" and "blind panic", had Scotland voted Yes, said Willie Rennie.

Mr Harvie attempted to answer the question, over how to manage declining North Sea oil reserves, but he was swimming against the tide. "I want to keep the Barnett formula today, tomorrow and forever," Mr Murphy added, hammering home his point after a token detour to fracking.

"I want us to have the ability in our own hands to have a decent welfare system," Ms Sturgeon hit back, arguing that Scotland should not be dependent on Westminster handouts or vulnerable to its cuts. "You have to be able to fund welfare", Ms Davidson retorted, pointing out that the IFS had predicted a £7.6bn financial black hole under the policy. "That's the other half of the equation Nicola that you don't want the people out there to know," she added.

Nobody was interested in laying a glove on Mr Harvie, so it was left to Mr Cook, who asked him whether he was saying that Green MPs would be unable to support a Government in favour of capitalism. He gave a knowing smile, before trying his best to dodge the question.

Notably, Ms Davidson also appeared to take a different line to the Prime Minister just hours earlier when he suggested the Tories would block a second referendum. "I do not see the circumstances where if the situation arose again we would," she said.

As the debate draw to a close, Mr Coburn returned to the fray, with Jim Murphy getting particularly animated. "You've made me furious," he cried, accusing him of demonising immigrants." Not to be outdone, Ms Sturgeon spoke of his "narrow minded xenophobic attitude.

But it was full fiscal autonomy, not Mr Coburn, that was the story of the night. Whether it proves a vote-winner (or loser) remains to be seen.