Who would you rather be this Xmas: Ed, Dave, Nick or Nige?

The 2015 general election is underway. Today, 19 December, the ‘long campaign’ begins, with limits on party spending, set by the Electoral Commission, coming into force. The ‘short campaign’ will begin on 30 March when Parliament is dissolved. The election will be 38 days later on 7 May.

Which political leaders can go home for Christmas with any reason to enjoy the festive cheer depends, to some extent, on which polls you believe. The fact is, they are all over the place this week.

Only yesterday I reported on the latest Guardian/ICM poll which gave the Conservatives their worst numbers in 18 months – falling behind Labour by five points.

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My headline observation – that George Osborne’s Autumn Statement was a political flop – I stand by: the Chancellor was meant to provide the Tories with a game-changer, and clearly he didn’t.

However, ICM’s five-point Labour lead was perhaps overly flattering to Ed Miliband, if you believe other polls released in the past 48 hours.

Yesterday’s Sun/YouGov poll had the Tories tied on 33 per cent while the Evening Standard/Ipsos-MORI December poll gave the Tories a three per cent lead over Labour, unchanged since November.

But today’s YouGov poll for the Sun gives Labour a five per cent lead, with 35 per cent to the Tories’ 30 per cent.

What’s happening? Some floating voters are clearly flip-flopping: Tories less sure about taking a gamble with Farage, for instance; Lib Dems inclined to vote Labour but unimpressed with Ed Miliband; others tempted to vote Green but – as they used to say of the Lib Dems – worried about wasting their vote.

Just as likely is that we are seeing the effects of the margins of error which apply to all polls. The safest course is to look at the average - and that shows a narrow Labour lead: just one or two per cent.

So, is it safe to make any predictions about what will happen on 7 May? I can offer only three certainties:

One. The next Prime Minister will be either David Cameron or Ed Miliband. (And the one who doesn’t make it will be bound to stand down as leader of his party.) Also, both men will keep their seats: neither Nick Clegg nor Nigel Farage can be certain they’ll even be MPs on 8 May.

Two. The head-to-head battle between Cameron and Miliband will be less important than their skirmishing with smaller parties. The Tories have lost votes to Ukip, for sure. But, as Harry Lambert writes for the New Statesman, they have lost almost no support to Labour. Neither has there been much switching from Labour to the Tories. So there is little scope for ‘defectors’ between the main parties to be won back to their former allegiance.

Three. The main losers in the election will be the current coalition partners. At the 2010 general election their combined share of the national vote was nearly 50 per cent (Tories 36, Lib Dems 23). Today their joint total is down around 40 per cent (Tories 33, Lib Dems eight), according to current polling averages. Labour, in comparison, are up four points on 2010.

So, what will the party leaders be most concerned about over the Christmas-New Year holiday?

David Cameron: Very simple – how to keep Ukip at bay. He will be delighted at the slump in Nigel Farage’s fortunes (see below). The Conservatives have found it almost impossible to actively discourage supporters from defecting to Ukip: they need Farage and his team to do the damage themselves. A series of rows and scandals has helped in this regard and it seems to be reflected in a drop in public ‘satisfaction’ with Farage.

Ed Miliband: The Labour party’s average one/two per cent lead over the Tories – down from an average six/seven per cent lead earlier in the year – makes it unlikely Labour will win a clear majority. But they are likely to be the biggest party and therefore in a position to either run a minority government or seek a pact of some sort with either the Lib Dems or the SNP. The biggest concern for Miliband is Scotland. At the 2010 election, Labour led the SNP by 42 per cent to 20 per cent. Latest polls show the situation reversed – with the Nationalists leading Labour by 47 per cent to Labour’s 27 per cent. Miliband is depending on the newly elected Scottish Labour leader, Jim Murphy, to claw back support.

Nick Clegg: The Lib Dem leader made an extraordinary impact in the 2010 TV debates – but his star has fallen the furthest. Of the 57 seats the Lib Dems won in the 2010 election, 27 are vulnerable to a swing of five per cent. And according to a recent Ashcroft poll, one of the seats they could lose is Clegg’s own constituency of Sheffield Hallam.

Nigel Farage: There’s no doubting the massive increase in Ukip’s appeal: they scored three per cent of the national vote in the 2010 general election and now average 15 per cent in opinion polls. But while they are stealing Tory voters, they are not doing as much damage to Labour as they profess, and the recent troubles in South Basildon appear to be hurting: according to Ipsos-MORI, Farage’s ‘satisfaction level’ is at an all-time low, with 33 per cent ‘satisfied’ and 53 per cent ‘dissatisfied’ giving him a minus 20 score. Only last month he came in at minus six. On top of all that, there is no guarantee that he will win Tory-held South Thanet, the Kent seat he has chosen to fight in May.

The Commons reopens for business on 6 January. It’s a good bet that many MPs will decide they are better off campaigning on their home patch, especially those in the key marginals. The election will be decided in around a fifth of the 650 parliamentary constituencies.

In the small hours of Friday 8 May whether the TV screens are awash with ‘Lab Gain’ or ‘Con Hold’ will depend on which party gets the most switchers from the Lib Dems and the fewest switchers to Ukip.