TV debate: It's a rammy at the BBC

It was a rather unedifying affair, descending several times into a rammy as the politicians were unable to resist shouting over each other as unfortunate host Gordon Brewer was relegated to the status of bystander.

The First Minister's proposal for Full Fiscal Autonomy, meaning Holyrood would become responsible for raising and spending all of its own cash, was first in the firing line.

How would she fill a £7.6 billion deficit, forecast by the Institute for Fiscal Studies? Labour have identified this SNP policy as the nationalist weak spot and see exploiting it as their best chance of turning the tide against harrowing ratings in the polls. Jim Murphy prepared for attack.

"This week we've seen the project fear campaign that dominated the referendum revived by these three unionist parties," the First Minister said, alleging that her opponents were trying to "talk down Scotland and assert we're not capable of not running our own affairs."

Ms Sturgeon said there were reasons not to accept the £7.6 billion figure, and that it would take several years to implement devo-max. The First Minister seemed to suggest that she would borrow the money initially, while gradually growing the economy.

Jim Murphy said the SNP leader was making "a dreadful point in a pretty reasonable way." A week ago, the pair had not met in front of the cameras since Scottish Labour elected its new leader. They have apparently grown to dislike each other intensely in that time, with Mr Murphy later accusing Ms Sturgeon of "showing herself up" on TV.

"Nicola is not entitled to her own facts," he said. "She's making this up as she goes along. To make this £7.6 billion up, Scotland would have to grow twice as fast as the advanced world... what's the magic policy you have that the rest of the world doesn't have?"

The two leaders both raised their voices as Ruth Davidson and Willie Rennie gave a knowing look to each other, perhaps aware of how this sort of thing goes down with voters at home.

"Gordon are you still here?" asked Mr Murphy of the host, after Willie Rennie branded the First Minister's plan economically irresponsible, sparking his own heated dispute with the First Minister. "I was beginning to wonder myself," he sighed.

The First Minister later refused to give a commitment to providing her own figures for how full fiscal autonomy would work ahead of the election. Jim Murphy said he feared a "pincer movement" between a Boris Johnson-led Conservative Party and the SNP would make Full Fiscal Autonomy, currently backed by none of the main Westminster parties meaning the nationalists would not have the votes to force it through, a reality.

Later, Ms Sturgeon said she was "not planning" for a second referendum during the lifetime of the next UK parliament, and that "something significant would have to change" for one to be proposed in next year's SNP manifesto for Holyrood.

Mr Murphy was later challenged over where Labour spending cuts, proposed by Ed Balls, would be made. "This is ridiculous" muttered the First Minister, as he said his party would "do some things differently," including cuts to MoD spending, child benefit freezes and winter fuel payments to rich pensioners.

When it was pointed out that the Charter for Budget Responsibility, which Labour had signed up to, meant £6 billion of cuts or tax rises, Mr Murphy claimed half of the total would come from increasing the top rate of tax. Ms Davidson pointed out that the IFS had estimated that the policy would raise between zero and £2 billion.

SNP campaign director Angus Robertson later accused the Labour chief of attempting to "cover up his cuts with bluff and bluster" after Ms Sturgeon had repeatedly accused Mr Murphy of dishonesty.

"Let Willie Rennie have a shot," said Mr Brewer, as the debate neared its conclusion. Perhaps wisely, the Lib Dem chief had chosen to remain on the sidelines for large parts of this slugfest.