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I know what you're thinking: let's talk Barnett formula.

I normally hesitate to go down that road as it's so comprehensively covered elsewhere but today's developments in Scotland have put the issue of how the UK funds its constituent parts centre stage.

The offer by the leaders of the three largest UK parties to preserve the formula will not go down well with those who believe it is too generous to the Scots and currently disadvantages the Welsh. Plaid Cymru's vocal response may be expected; the views of a Labour parliamentary candidate and former AM less so.

, who is fighting Carmarthen West and South Pembrokeshire next May, tweeted: "Vow to retain Barnett is wrong and will foster resentment. Blind panic not a good basis for constitutional reform. Salmond wins either way."

The key question appears to be whether a promise to keep the formula for Scotland would prevent a UK government changing the formula.

A Welsh Labour spokesperson said: "Our position is clear - the current settlement is unfair to Wales and must be reformed. Ed Miliband said he recognised this and would seek to address the fair funding issue in a future Labour Government. This should not be seen as a zero sum game, we don't want the resolution of underfunding to damage the Scottish budget."

Sceptics might suggest that "seeking to address" an issue isn't quite the "vow" made in Scotland today. It's now four years since George Osborne, then shadow chancellor, visited Cardiff to say: "My initial look at the formula suggests that Wales might well be missing out under the Barnett arrangements. I think it is in Wales' interest that we have that needs-based assessment, which is independently done… my view is that you want to move on it pretty quickly, as soon as a new government is elected."

At the time (February 2010), the then head of the IWA think tank declared this as t

What happened next? Mr Osborne became chancellor in a coalition government with the Liberal Democrats, who went into the 2010 general election committed to a fair funding formula. Once in office, both the Conservatives and Lib Dems said the priority had to be balancing the UK's books. Earlier this month, the Liberal Democrats updated their pledge with a pre-manifesto promise to "seek [that word again] over a [five-year] parliament to increase the Welsh block grant to an equitable level".

David Cameron suggested six years ago that the formula's days were numbered and he has consistently said .

Yet, the remarkably resilient formula is still with us, as indeed is Lord Barnett, the Labour former chief secretary to the Treasury after whom the formula is named. Joel Barnett celebrates his 91st birthday next month. He has long argued that the formula wasn't supposed to last this long and that it should be reformed, although I suspect he is still rather flattered by the linking of his name to a formula that is still being discussed 30 years later.