THE period between September 18 2014 and March 24 2016 could prove to be the longest 18 months in Scotland's political history.

This, we are told, is the period in which the Scottish Government will have to complete Scotland's transition to full independence, if voters say Yes in the autumn.

Now Hell (in America) may have frozen over this month but completing such a gargantuan task in such a comparatively short space of time looks a tad over-ambitious.

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In this timescale, Alex Salmond and his colleagues will have to: unpick a 300-year-old Union with England and negotiate a myriad of deals with Whitehall; work their way through a wealth of international treaties; join the European Union by agreement of all the other 28 member states; become a member of Nato, the United Nations, the Commonwealth and so on.

A few weeks ago, Angus Robertson, the Nationalist leader at Westminster, suggested it would be rather a good idea to put back the May 2015 General Election because it would prove a diversion to the negotiations.

This contender for understatement of the year belies a deep-seated worry at Bute House.

By grandly announcing a date for Independence Day, the First Minister has boxed himself in; never a good ploy in complex negotiations.

Whitehall sources have already made clear they cannot believe the SNP chief has made such a fundamental error.

As intergovernmental talks became fraught on issues such as debt, currency union and Trident, it would be in the UK Government's interests to drag things out. "We'd just sit on our hands," said a senior Coalition source.

What also lay beneath Mr Robertson's suggestion was the prospect of an SNP Government beginning negotiations with one UK Government - a Lib-Con Coalition - and then within six months having to negotiate with another, say, a Labour administration.

The nature of the 2015 poll would be transformed by a Yes vote. As intergovernmental negotiations dragged on, there would undoubtedly be pressure south of the border to get tough with the demanding Scots on a raft of measures.

It could be that a Labour government would be elected on a ticket to reverse some of the things already agreed by Messrs Cameron and Clegg.

A number of top legal experts this week, who suggested the 18-month timescale was "ludicrous", made clear that on the back of an election mandate a new UK Government would be entitled to scrap any deals with Edinburgh and start again.

The top academics were asked a straightforward question: what would happen if, come March 24 2016, there was no agreement? The pregnant pause lasted several seconds before one suggested: "Chaos."

To keep to his 18-month timescale would Mr Salmond be willing to make more concessions? How would voters react? By contrast, with a General Election looming, David Cameron would be under electoral pressure to concede nothing to get back into Downing Street.

And, if the negotiations were not going well, Scots, who just a few months before had opted for independence, might as things unfolded, begin to think they had made a big mistake.

One of the constitutional experts even suggested this could lead to, ahem, a second referendum. Hell couldn't freeze over twice, could it?