The pattern is becoming familiar. On Mondays the Tories surge. Then at around 10.30pm that evening, it turns out that the two main parties are at deadlock. At the end of the week, Labour charges ahead.
The way polls are interpreted is increasingly driven by each pollsters’ release schedule rather than by any substantial change in the underlying trends.
Or so it has seemed until now.
A closer look at the figures reveals that some clear trends have emerged over the past two weeks. Clarity does not of course imply certainty – but here’s what we know, and don’t know, with just a week to the election.
1. The Conservatives have edged ahead in the polls and are more likely to be the largest party
Polls this week have ranged from a Conservative six-point lead to a Labour three-point advantage.
That is a significant difference, and there is some debate as to why there is such divergence between different polls.
One explanation has been the differing methods between phone and internet polls, with the latter showing higher Labour scores and higher Ukip ones, while the former produces higher Conservative numbers and lower ones for Nigel Farage’s party.
A second suggestion has been that the difference between the results is produced by more established firms compared with newer pollsters.
Although there is evidence to support both theories, there are also differences within both groups to suggest that the answer to the enigma may in fact be found elsewhere.
If we focus not on the size of the Tory (or Labour) leads, but instead at the relative vote share of the two parties, the gap between the two contenders is far more stable than may initially meet the eye.
The range for the Tories (calculated from the average of figures released by each individual polling company during the campaign) is 32.5–35.5%, compared with Labour’s 32–34.5%.
So either at the top or the bottom end of those ranges, the Conservatives are slightly ahead. It’s not a large lead in either case, but it is real.
Of course there isn’t a consensus among all the polls, and the one set of figures that seems to counter the pack one day, may end up being the most accurate snapshot in a week’s time.
However, as things stand, the trend is that the Tories are more likely than not to emerge as the largest party on 7 May.
2. Scotland will produce an SNP landslide
In Scotland, the polls have been far easier to interpret. Phone polls, internet surveys and constituency polling, all say the same thing: the SNP is on course to winning most of Scotland’s 59 seats.
If anything the SNP lead is increasing – three polls this week have them above 50% of the vote.
In the Guardian’s projection, Nicola Sturgeon’s party is set to gain 49 seats, which added to their existing tally means there would be 55 SNP MPs in the next parliament.
3. The coalition arithmetic still favours Miliband over Cameron
Although the evidence and trend suggests that the Conservatives will be the largest party, having the numbers to form a government is a different matter all together.
The arithmetic and paths that lead to No 10 still lean towards Miliband despite the Tories’ lead in the polls.
Because it is extremely unlikely that a single party will have an outright majority, both Cameron and Miliband would need the votes of other parties if they are to command the confidence of the House of Commons.
The SNP, Plaid Cymru, the Greens and the SDLP have all said they would vote a Tory government down – and together with Labour – this bloc adds up to 331 seats, compared with Cameron’s 313 (assuming the Tory leader can indeed cobble together a deal that includes the Lib Dems, Ukip and the DUP).
The problem for the Conservatives is that any seat the SNP takes away from Labour makes no difference to the anti-Tory bloc’s total. However, the 10 seats the SNP are projected to gain from the Lib Dems and the Scottish Conservatives hurts the Cameron bloc.
The hard truth is that the Conservatives would need to roughly cut by a third the 41 seats the party is currently projected to lose to Labour – and currently there is no evidence to suggest that they will.
There are of course political considerations alongside the figures, but these are the numbers.
Unless Cameron can open up at least a four or five point lead in the polls in the last week of campaigning, the inevitability that follows the maths will eventually mean he can no longer continue as prime minister.
4. The great unknown: the Ukip vote
The single most uncertain factor on 7 May is the Ukip vote.
Although Ukip ranges from 10% to 18% in the polls, support for Nigel Farage’s party has been dropping steadily since the beginning of the year. In January it averaged 15%. It is now below 13%. The direction of travel is also apparent in Lord Ashcroft’s constituency polling.
However, this doesn’t tell us enough.
What will decide Cameron and Miliband’s electoral prospects isn’t so much the national share of the vote that Farage’s party captures. Instead the first issue is how the votes are distributed in marginal Tory-Labour seats. Secondly, if there is indeed a swing away from Ukip in these seats, who will benefit more between the Conservatives and Labour.
With a week until the election, the Tories narrowly lead in the contest for largest party, and Miliband is marginally ahead in the race to No 10 – but make no mistake: the differences are so minor that neither game is over.
This article was written by Alberto Nardelli, for theguardian.com on Thursday 30th April 2015 07.00 Europe/Londonguardian.co.uk © Guardian News and Media Limited 2010