TODAY marks 100 days until the General Election. The polls suggest the race for Downing Street will go down to wire. All we can predict with any confidence is one of the closest contests since the war.

The 2015 campaign will matter more than most. The parties may well fight each other to a standstill over the coming 14 weeks; Messrs Cameron and Miliband could arrive at polling day neck and neck in the polls, just as they have spent the last year or so. But the battle we are about to witness could mean the difference not just between a large majority or a slender one, but between defeat or victory itself.

The parties have rarely been under greater pressure to get their messages right, to explain their competing visions convincingly and passionately and to read the public mood accurately. How they respond to the rigours of the coming months could determine very different futures for the country over the coming five years.

A clear picture of the contest is already emerging. The biggest difference between David Cameron and Ed Miliband - we can be reasonably sure one of them will be Prime Minister after May 7 - is economic. In terms of hard cash, the Conservatives' will cut £33billion per year to reduce the deficit, according to the IFS think tank, while Labour's target means cuts of £7billion per year.

The Conservatives stand accused of imposing a callous austerity on the country, Labour of endangering slow but healthy economic growth through profligacy and fiscal indiscipline.

Other issues are also at stake, however. The state of the health service in all parts of the UK will be a factor. Labour's pledge to invest an extra £2.5billion would generate a £250million share for Scotland. Unless you believe the Conservatives, of course, who say the figures are unaffordable: a sign of Mr Miliband's economic recklessness.

These are matters for whole of the UK to consider. Other parts of the debate will be very different in Scotland. While south of the Border the Conservatives and Labour are pushed on immigration by Nigel Farage's UKIP, here the questions of devolution will be to the fore.

The SNP, riding high in the polls, hope to hold the balance of power and use their influence to demand devo max - Holyrood control over everything but defence and foreign affairs - and an end to nuclear weapons. How effectively the Nationalists campaign could decide the outcome of the whole election.

A ComRes poll today puts the Conservatives in the lead by a single point. No one party, however, is likely to stay out in front from here to polling day. The campaign is only just beginning.

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