Predicting Seat Levels in the 2017 UK General Election based on recent Opinion Poll Figures (19th April 2017)

Adrian Kavanagh, 19th April 2017

Following an announcement by Theresa May yesterday and a House of Commons vote to confirm this today, a “snap” general election is now scheduled to be held in the United Kingdom on Thursday 8th June 2017. What do the latest opinion poll figures suggest in relation to the likely number of seats that each party will win in that contest? As the last general election in the United Kingdom showed, this is a hazardous task to engage in, as the votes to seats ration can be skewed by geography and spatial differences in terms of support gains/losses for the different parties. For instance, Labour’s overall share of the vote increased in 2015, relative to the 2010 General Election, by 1.5%, but the extent of the party’s support/seat losses to the Scottish Nationalist Party in Scotland (returning with just 1 of the 41 seats that the party had won there in 2010) meant that most of the 701,147 votes won by Labour in Scotland were effectively wasted votes.  

For the purposes of this analysis, I have averaged out the estimated support levels for the five political parties in the United Kingdom (Conservatives, Labour, United Kingdom Independence Party, Liberal Democrats and the Green Party) that are covered in all of these polls. As no consistently accurate poll figures are presented here for the regional parties, or for the very small parties, I have assumed – for the purposes of this model – that support levels for these parties/groupings will remain “as was” relative to the 2015 contest. Averaging out the party support estimates in the most recent ICM/Guardian, Opinium/Observer, ComRes/Independent/Sunday Mirror and You Gov/Times opinion polls (as published on the UK Polling Report website) estimates support levels for these five parties to stand as follows: Conservatives 43.5% (up by 6.7% relative to 2015), Labour 25.5% (down by 5.0% relative to 2015), United Kingdom Independence Party 10.3% (down by 2.4% relative to 2015), Liberal Democrats 10.3% (up by 2.1% relative to 2015) and Green Party 4.3% (up by 0.6% relative to 2015).

Using the same constituency-level analysis model that I employ to study the likely impact of Irish opinion poll figures on Dail-seat estimates, I estimate the following number of seats would be won by these parties – and other parties in England, Scotland and Wales – in June 2017, should the latest opinion poll figures be replicated exactly at the general election contest: Conservatives 374 (up by 44 seats relative to 2015)Labour Party 183 (down by 49 relative to 2015)Scottish Nationalist Party 55 (down by 1 relative to 2015)Liberal Democrats 13 (up by 5 relative to 2015)Plaid Cymru 4 (up by 1 relative to 2015), Green Party 2 (up by 1 relative to 2015) and United Kingdom Independence Party (down by 1 relative to 2015). (As the national-level opinion poll figures seem to largely ignore Northern Ireland, I cannot factor in support/seat estimates for the political parties in Northern Ireland into this analysis, unfortunately.)

The model predicts that the Conservative Party would gain seats in the following 44 constituencies:

Alyn & Deeside
Barrow & Furness
Batley & Spen
Berwickshire, Roxburgh & Selkirk
Birmingham Northfield
Bishop Auckland
Blackpool South
Bolton North East
Brentford & Isleworth
Bridgend
Bristol East
Bury South
Chester, City of
Clacton
Ellesmere Port and Neston
Eltham
Enfield North
Exeter
Gedling
Halifax
Hammersmith
Hampstead and Kilburn
Harrow West
Hove
Hyndburn
Ilford North
Lancaster and Fleetwood
Mansfield
Middlesbrough South and East Cleveland
Newcastle-under-Lyme
Newport West
North East Derbyshire
Plymouth, Moor View
Scunthorpe
Southampton, Test
Stoke-on-Trent South
Tooting
Wakefield
Walsall North
Westminster North
Wirral South
Wirral West
Wolverhampton South West
Workington

Most of these gains would be made at the expense of the Labour Party, but gains would also come at the expense of the United Kingdom Independence Party (Clacton) and the Scottish Nationalist Party (Berwickshire, Roxburgh & Selkirk), should the support/seat estimates in this analysis pan out in the actual general election in June 2017. The model, however, also does predict that the Conservatives would lose the constituency of Lewes to the Liberal Democrats.

The model predicts that Labour would lose seats in the following constituencies – with most of these losses being made to the Conservatives, but with losses also predicted to be made at the expense of the Liberal Democrats, Plaid Cymru and the Green Party (see below):

Alyn & Deeside
Barrow & Furness
Batley & Spen
Birmingham Northfield
Bishop Auckland
Blackpool South
Bolton North East
Brentford & Isleworth
Bridgend
Bristol East
Bury South
Chester, City of
Ellesmere Port and Neston
Eltham
Enfield North
Exeter
Gedling
Halifax
Hammersmith
Hampstead and Kilburn
Harrow West
Hove
Hyndburn
Ilford North
Lancaster and Fleetwood
Mansfield
Middlesbrough South and East Cleveland
Newcastle-under-Lyme
Newport West
North East Derbyshire
Plymouth, Moor View
Scunthorpe
Southampton, Test
Stoke-on-Trent South
Tooting
Wakefield
Walsall North
Westminster North
Wirral South
Wirral West
Wolverhampton South West
Workington
Bermondsey & Old Southwark
Bristol West
Burnley
Cambridge
Cardiff Central   (and also Wrexham)
Ynys Môn

The model predicts that the Liberal Democrats would make gains in the Bermondsey & Old Southwark, Burnley, Cambridge and Cardiff Central constituencies at the expense of the Labour Party, while also taking Lewes from the Conservatives.  The Green Party is predicted to gain a second seat in Bristol West, again at the expense of Labour, while Plain Cymru are also predicted to take Ynys Môn from Labour.

How this model works: As with my analyses of opinion poll figures in Ireland, constituency support estimates for different parties and groupings form the basis of the general approach taken with this analysis. This approach seeks to ask the following question in relation to different opinion poll results – what do these poll figures mean in terms of the likely number of House of Commons seats that could be won by the different parties and groupings on those national support levels? As the electoral system employed in the United Kingdom is most definitely not a proportional electoral system, the proportion of seats won by parties will not measure up exactly to their actual share of the first preference votes. Geography will have a very significant impact here, while first past the post electoral systems, such as the one used in the United Kingdom, will always act to the advantage of the largest parties and will significantly disadvantage the smaller parties, unless their votes are strongly clustered in a specific geographical region – e.g. Scotland, Wales or Northern Ireland.

First preference votes need to be filtered through the system of the United Kingdom’s general election constituencies . In order to address the question, I estimate what the party first preference votes would be in the different constituencies, assuming similar (proportional) changes in party vote shares in all constituencies to those that are being suggested by a particular opinion poll, or – in this case – an average of the most recent polls. This of course is a very rough model and it cannot take appropriate account of the fact that changing support levels between elections tend to vary geographically 9as occurred in the 2015 contest). Thus constituency support estimates for different parties/groupings will be over-estimated in some constituencies and under-estimated in others, but the expectation would be that the overall national seat figures figures estimated will be relatively close to the true level, given that over-estimates in certain constituencies will be offset by under-estimates in others. Based on these estimated constituency support figures, I proceed to estimate the destination of seats in the different constituencies. Due to unusually high/low support levels for some parties or political groupings in certain constituencies in the previous election, the model may throw up occasional constituency predictions that are unlikely to pan out in a “real election”, but of course the estimates here cannot be seen as highly accurate estimates of support levels at the constituency level as in a “real election” party support changes will vary significantly across constituency given uneven geographical shifts in support levels.

The point to remember here is that the ultimate aim of this model is to get an overall, national-level, estimate of seat numbers and these are based, as noted earlier, on the proviso that an over-prediction in one constituency may be offset by an under-prediction in another constituency. This model does not aim, or expect, to produce 100% accurate party support and seat level predictions for each of the 650 constituencies. These analyses simply estimate what party seat levels would be, should such national support trends be replicated in an actual general election. For a variety of reasons (including the impact of high levels of undecided voters in a specific poll), the actual result of an election contest may vary from the figures suggested by an opinion poll, even if the poll is carried out relatively close to election day, or on election day itself as in the case of exit polls, but the likelihood of such variation is not something that can be factored into this model.

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About Adrian Kavanagh

Lecturer in Maynooth University Department of Geography.
This entry was posted in opinion polls, Scotland, United Kingdom and tagged , . Bookmark the permalink.

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