Three scenarios for the 2015 election based on current polling: which do you think looks most plausible?

by Stephen Tall on December 10, 2013

In 18 months we’ll know the result of the 2015 general election.

Forecasting is a mug’s game – especially because there are an even greater number of variables this time than usual: a governing coalition of two parties with one established centre-left opposition, Labour, and an insurgent right-wing party, Ukip.

But plenty are having a go at it anyway. Lib Dem MP Sir Nick Harvey reckons Labour has the next election in the bag. Psephologist Lewis Baston thinks we’re headed for a second hung parliament. And pollster Sir Bob Worcester believes the Lib Dems are destined for meltdown.

Here’s my quick ‘n’ dirty analysis based on the polling trends. What I’ve looked at is Labour’s lead over the Conservatives according to the monthly average of opinion polls under three different scenarios.

(Huge caveat straight off: the extent of the polling science on display here is me playing around on an Excel spreadsheet.)

Scenario 1

The Conservatives hit rock bottom in May 2012. The omnishambles budget and its desperate U-turns were followed by a poor set of local election results. There have been dips since then, notably when it looked like the economy might plunge into what was being billed as a triple-dip recession at the start of 2013, but never quite matching that period.

Taking May 2012 as the peak of Labour’s lead, what would happen if the linear trend since then were to continue through to May 2015? This is what:

polling trends 2015 - ST 2

Under Scenario 1, then, the Conservatives would have recovered to be within 2% of Labour by the time of the next general election. That would most likely point to a hung parliament, though if Labour out-performs in the marginals they could well sneak a Commons majority.

Coincidentally this is the gap forecast by Lewis Baston, who predicts a Lab 36% – Con 34% result. It feels about right to me – but, as ever when looking at data, beware confirmation bias…

Scenario 2

May 2012 is a pretty arbitrary cut-off point – so let’s take another arbitrary cut-off point: the calendar year. If we just look at 2013 – from January 2013 (pretty much the mid-point of this parliament) to November 2013 – and project forwards, what happens? Here’s what:

polling trends 2015 - ST 1

Under Scenario 2, then, the Conservatives would move into a clear lead over Labour of 4% by the time of the next general election.

I don’t think there’s a single Tory who wouldn’t take that result right now – though it’s very unlikely to translate into an outright Conservative victory. After all, the Tories led Labour by 7% in 2010 and still feel short.

Scenario 3

File this under the heading “a bit of fun… probably” – let’s look at the whole parliament and insert a polynomial trendline to take us through to May 2015. Here’s what happens:

polling trends 2015 - ST 3

Under Scenario 3, then, the Conservatives bounce back from their mid-term slump to lead Labour by 6% come the next general election. It couldn’t happen – could it?

So there you go… Three scenarios based on the tends from current polling. Which – if any – do you think looks most likely?

* Stephen Tall is Co-Editor of Liberal Democrat Voice, and editor of the 2013 publication, The Coalition and Beyond: Liberal Reforms for the Decade Ahead. He is also a Research Associate for the liberal think-tank CentreForum and writes at his own site, The Collected Stephen Tall.