THE uneasy referendum alliance between Labour, the Conservatives and Liberal Democrats seems a long time ago. The general election gloves came off before the Christmas decorations came down and the three main UK parties are trading blows with increasing hostility.

The truce lasted long enough, however, for them to utter a final, common, post-referendum plea. "Move on," was the plaintive cry. "Stop fighting the referendum campaign," they begged the Nationalists. "Accept the result. Let's talk about something - anything - else."

There was a note of desperation to it all. As the heady elixir of defeat sent the SNP's membership soaring and post-referendum polls showed majority support for Yes, the pro-UK parties really did feel as if they had won the battle but lost the war.

The SNP remain in a formidably strong position. They enter the election battle nearly 20 points ahead of their main rivals Labour, a lead that would deliver them 45 of Scotland's 59 Westminster seats on a uniform swing.

But since MSPs have returned to Holyrood after their festive break, it has been possible to detect a more optimistic mood among the Nats' opponents. There is a simple enough explanation: oil prices.

The fall in world oil prices from $110 per barrel last June to below $50 has reopened all the difficult questions about an independent Scotland's economic prospects that were aired during the referendum campaign.

Unionist MSPs are openly speculating what the referendum result might be if the vote were tomorrow, rather than four months ago. Suffice to say, they do not believe it would be as close as 55 per cent to 45 per cent. Suddenly, their squeals of "stop fighting the referendum campaign" have fallen silent. Indeed, the pro-UK parties are joining battle with a gusto they rarely mustered last year.

What has fired them up is the SNP's decision to fight the election on a devo max ticket. The moment Alex Salmond, backed by Nicola Sturgeon, declared the SNP would demand Holyrood control over all policy areas bar defence and foreign affairs if they hold the balance of power after the election, the heavily artillery was wheeled out. It arrived in the shape of Treasury figures showing an £18.6billion gap between Scotland's North Sea revenues with oil at $50 per barrel and with the Scottish Government's forecast of $113 per barrel, from 2016 to 2019.

The Conservatives fumed about a government decision to stop publishing oil forecasts. Labour highlighted the impact of losing the Barnett Formula under a devo max set-up, quoting the SNP's own warnings it would cost Scotland £4billion. The SNP hit back, insisting oil prices would return to $110 per barrel soon enough and, in any case, the North Sea was a "bonus" rather than the basis of Scotland's economy.

It seems all the parties are confident a re-run of the referendum will work for them in the battle for votes on May 7. What was billed as the most contest since the war is starting to look like the deja vu election in Scotland.

ends