General Election blog: Labour's formula for attacking the SNP

"What do we want?" "The Barnett formula!" "When do we want it?" "Now. And forever!"

As political slogans go, it's not the most catchy.

Hard to imagine fist-waving Labour activists chanting it as they march in their angry thousands on Holyrood.

Yet, slightly parodied I confess, a call to arms over Scotland's funding was one of the key messages of Labour Scottish manifesto launch today.

Labour sees the future of Barnett formula as one of the big issues to attack the Scottish National Party over.

Quick aside for non-anoraks: the formula is named after Joel Barnett the Labour Treasury chief secretary in the Callaghan government who came up with it in the late 1970s.

It gives Scotland a share of the spending allocated south of the Border in areas which are now devolved like health and education.

It has resulted in spending per head in Scotland being higher than the UK average, something UKIP in this election, and some English Tory MPs in the past, dislike.

With apologies for the diversion into detail, necessary though it is, back to the politics.

Labour has the SNP's desire for full fiscal autonomy in its sights.

Sorry more jargon but FFA, to give it its abbreviation, essentially means Scotland raising all its taxes and deciding all its spending but within the UK.

Labour cite the respected Institute for Fiscal Studies saying that FFA would leave a gap of £7.6 billion in Scotland's finances.

That figure is accurate. You can see the IFS report here:http://www.ifs.org.uk/publications/7652

And using that report, this is how Mr Murphy put it today in his speech at the manifesto launch in Glasgow:

"The Barnett Formula adds up to hundreds of pounds more for every Scot, spent on schools and hospitals. And I want to be clear that Labour will defend Barnett today, tomorrow and forever. Throughout our manifesto and in my speech, the value of Barnett is clear."

It is significant Labour has put such an emphasis on something which, it is reasonable to suggest, most Scots have little or no detailed knowledge of.

Indeed, Mr Murphy himself admitted the Barnett formula was rather like a "long forgotten maths lesson". But that did not stop him trying to educate the Scottish electorate.

Without this funding Scotland's NHS would, among other services, be jeopardised, he claimed.

The SNP of course dispute this.

They say that fiscal autonomy would, to take one benefit, allow them to grow Scotland economy faster.

They also say it would take several years to introduce, and the IFS figure is just a snap-shot.

I'll come back to the SNP when they launch their manifesto but funding of Scotland, and the Nationalist's plans have become a key battleground.

Mr Murphy had another key message: the only way, he claimed, to get David Cameron out of Downing Street was to vote Labour.

The trouble for Mr Murphy is that the SNP - currently consistently way ahead of Labour in the polls - have a different message.

If the SNP do as well as the polls suggest, and that is still an 'if', then they will hold the balance of power.

As Nicola Sturgeon put it in the BBC debate last night they can help "lock David Cameron out of Downing Street".

The SNP leader also won applause from the London audience for saying that if Ed Miliband turned his back of the chance to get rid of the Tories "people would never forgive you".

So the battle for the left-of-centre vote and the consequences of voting either SNP or Labour is another big issue north of the Border ahead of May 7.

Finally, given the state of the polls in Scotland, it is worth reminding ourselves what happened between Labour and the SNP at the last UK election.

In 2010 Labour won 41 seats, taking 42% of the vote. A total of 1,035,528 people voted Labour. Their vote increased by 2.5%.

The SNP won just 6 seats, taking 19.9% of the vote. A total of 491,386 people voted for the Nationalists. Their vote increased by 2.3%.

Labour hopes it can pull back the SNP lead in the polls over the next couple of weeks. Even if it manages to do so, a repeat of the 2010 result is very, very, very, unlikely.