The 12 May Opinion Poll

Today has seen YouGov publish its opinion poll for The Sunday Times.

A brief guide to how I analyse this:

• The key part of the data is how the vote shifts from party to party. Now, some of this is shifts to Plaid Cymru and the Scottish National Party (treated together in the poll). What I do is to draw up separate England and a Wales & Scotland transfers - if you know that x% of voters for party A transfer to Plaid Cymru/Scottish National Party then these must be in the Wales & Scotland section.
• The Greens are an interesting option - contest too many seats to be a fringe party, yet contest too few seats to be a major party. I work out the number of voters to be transferred to the Greens - if there were a Green candidate at the May 2010 general election then they are transferred; if not they remain with their party
• Then there are regional adjustments made so that if a party is listed in the opinion poll as having 20% of the vote in a region, but the calculations show 19%, then its vote is increased across all seats there to match this - I only do this for the Conservatives, Labour, Liberal Democrats, Scottish National Party and UK Independence Party

For the regions used, it is obvious what is meant by London and Scotland. I am taking Rest of South to mean Eastern England, South East England and South West England; Midlands/Wales to mean East Midlands, Wales and West Midlands; and North to mean North East England, North West England and Yorkshire & the Humber.

Note that we are dealing with averages - there will be things like incumbency factors and local issues that allow seats to buck the trend.

At the 2010 general election, the result was:

• Conservatives - 306 (including 1 Deputy Speaker)
• Labour - 258 (including 2 Deputy Speakers)
• Liberal Democrats - 57
• Northern Ireland parties - 18
• Scottish National Party - 6
• Plaid Cymru - 3
• Greens - 1
• The Speaker - 1

If we take the changes in vote, then we get:

• Labour gains 111 seats from the Conservatives, 27 from the Liberal Democrats and 1 from the Greens - a net gain of 139 seats
• Plaid Cymru gains 1 seat from the Liberal Democrats
• Kidderminster Hospital & Health Concern gains 1 seat from the Conservatives
• The Greens lose 1 seat to Labour
• The Conservatives gain 24 seats from the Liberal Democrats but lose 1 to Kidderminster Hospital & Health Concern, 1 to the Liberal Democrats and 111 to Lanour - a net loss of 89 seats
• The Liberal Democrats gain 1 seat from the Conservatives, but lose 1 seat to Plaid Cymru, 27 to Labour and 24 to the Conservatives - a net loss of 51 seats

This gives us:

• Labour - 397 (including 2 Deputy Speakers)
• Conservatives - 217 (including 1 Deputy Speaker)
• Northern Ireland parties - 18
• Liberal Democrats - 6
• Scottish National Party - 6
• Plaid Cymru - 4
• Kidderminster Hospital & Health Concern - 1
• The Speaker - 1

So, a clear Labour majority of 144.

In more detail, there would be Cabinet casualties. 4 Conservative Cabinet members lose to Labour - Work & Pensions Secretary (and former party leader) Iain Duncan-Smith in Chingford & Woodford Green, International Development Secretary Justine Greening in Putney, Welsh Secretary David Jones in Clwyd West (which becomes a close 3-way Labour/Conservative/Plaid Cymru marginal, which would be Plaid Cymru's third top target seat) and Northern Ireland Secretary Theresa Villiers in Chipping Barnet.

In addition there would be 3 Liberal Democrat Cabinet ministers defeated - Scottish Secretary Michael Moore would lose Berwickshire, Roxburgh & Selkirk to the Conservatives (where he would be about 200 votes ahead of third-placed Labour), while Lord President of the Council Nick Clegg and Chief Secretary to the Treasury Danny Alexander would lose Sheffield Hallam and Inverness, Nairn, Badenoch & Strathspey respectively to Labour. Clegg would plunge to fourth place as the UK Independence Party comes third in what becomes a Labour/Conservative marginal. Alexander can console himself with runner-up status, about 200 votes ahead of the Scottish National Party and about 500 ahead of the Conservatives.

This means 2 Liberal Democrat Cabinet ministers survive the election - Business Secretary Vince Cable in Twickenham (a seat where Labour overtakes the Conservatives) and Energy & Climate Change Secretary Ed Davey in Kingston & Surbiton (another seat with Labour coming second). Cable and Davey would get the first and second highest Liberal Democrat share of the vote respectively.

In the House of Commons they would be joined by just 3 other political survivors - Deputy Leader of the House of Commons Tom Brake in Carshalton & Wallington, Paul Burstow in Sutton & Cheam and Deputy Chief Whip Alistair Carmichael in Orkney & Shetland. In addition, the Liberal Democrat who unseated the Conservatives' Zac Goldsmith in Richmond Park would join the experienced MPs - which might be a relief to Prime Minister David Cameron.

In the October 1951 and May 1955 general elections the Liberals were reduced to 6 MPs - but this time it'll be the "South West London fringe" rather than the "Celtic fringe".

Apart from Orkney & Shetland their best non-London result would be former leader Charles Kennedy in Ross, Skye & Lochaber, where he would narrowly lose to Labour. This would be the Greens' second top target seat, even though they would be sixth (with the Conservatives third, Scottish National party fourth and the UK Independence Party fifth - this would be the seat with the smallest gap between the first and sixth placed candidates)

My hunch is that in these circumstances Davey would beoome leader - he's fairly young and would have worked in Government on an issue close to every Liberal Democrat's heart.

Although the UK Independence Party won't win any seats, they would come second to the Conservatives in 3 seats - Christchurch, Herefordshire North and South Holland & the Deepings - and the runner-up to Labour in Birmingham Ladywood (which is one of their worst results in terms of share of the vote - but that's four-party politics for you! They just don't do as badly as the Conservatives or the Liberal Democrats there)

None of these are the seat where they get their highest share of the vote (although South Holland & the Deepings is where they get their second highest share of the vote, and Christchurch where they get their third) - that goes to South Holland & the Deepings' next-door neighbour Boston & Skegness, which becomes a 3-way Conservative/Labour/UK Independence Party marginal, and would be the only seat where they get over a quarter of the vote. This would be their third top target seat.

With the rise of multi-party politics, there would be some 4-way marginals, where less than 10% of the vote separates the top 4 candidates. These would be:

• Bromley & Chislehurst (Conservative hold) - a Conservative/Labour/Liberal Democrat/UK Independence Party 4-way marginal, where 8.15% separates the first and fourth places
• Croydon South (Labour gain from Conservative) - a Labour/Conservative/Liberal Democrat/UK Independence Party 4-way marginal, where 8.64% separates the first and fourth places
• Montgomeryshire (Conservative hold) - a Conservative/Labour/Plaid Cymru/UK Independence Party 4-way marginal, where 8.83% separates the first and fourth places

Bromley & Chislehurst would be the UK Independence Party's second top target seat - their top target would be Hornchurch & Upminster, where they would be in third place and needing a 3.19% swing to win the seat from Labour (curiously, last year there was speculation that the sitting Conservative MP for Hornchurch & Upminster, Angela Watkinson, would defect to the UK Independence Party).

Croydon South is an interesting seat - the Conservative MP, Richard Ottaway, is retiring, leading to speculation that Mayor of London Boris Johnson would be the Conservative candidate.

Montgomeryshire would be the Conservatives' sole Welsh seat - the others they have at the moment (Aberconwy, Cardiff North, Carmarthen West & South Pembrokeshire, Clwyd West (see above), Monmouth, Preseli Pembrokeshire and Vale of Glamorgan) all fall to Labour, although in Aberconwy they would be pushed into third place by Plaid Cymru, with this becoming Plaid Cymru's second top target seat.

Montgomeryshire would be Plaid Cymru's fifth top target seat, the UK Independence Party's top Welsh target seat (as well as their seventh top target nationally, just behind Old Bexley & Sidcup, which becomes a close Conservative/Labour marginal) and the Welsh seat where they get their highest share of the vote, as well as the seat with the closest gap between the first placed candidate and the fifth - in this case the Liberal Democrats, who get the highest share of the vote for any fifth placed candidate.

The Conservatives' result at least is one Welsh seat more than the Liberal Democrats, who lose Brecon & Radnorshire to Labour (and fall to fourth place as this becomes a Labour/Conservative marginal with the UK Independence Party in third place), Cardiff Central to Labour (and are pushed into third place by the Conservatives and end up about 40 votes ahead of the fourth placed UK Independence Party), and Ceredigion to Plaid Cymru (with Labour pushing the Liberal Democrats into third place).

For Plaid Cymru, holding onto their existing 3 seats, the top target seat would be Ynys Môn . The second and third (Aberconwy; Clwyd West) have been mentioned, and fourth would be Llanelli - Ynys Môn and Llanelli would both be seats where there would not be a significant Conservative vote, enabling a straight Labour/Plaid Cymru fight.

Other minor parties and independents coming second would be Respect - The Unity Coalition being the runner-up to Labour in Birmingham Hall Green and Poplar & Limehouse; an Independent would come second to the Conservatives in Castle Point; the Buckinghamshire Campaign for Democracy would come second to the Speaker in Buckingham; People's Voice for Blaenau Gwent come second to Labour in Blaenau Gwent; the British National Party come a distant second to Labour in Barking; and last but not least, Green MP Caroline Lucas would lose to Labour in Brighton Pavilion (which becomes the Greens' top target seat).

We have seen that in Scotland, the Liberal Democrats would be down to just one seat - Orkney & Shetland. Aberdeenshire West & Kincardine would fall to the Conservatives (with Labour pushing the Liberal Democrats into third place), Argyll & Bute would fall to Labour (with the Liberal Democrats in fourth place as the Scottish National Party comes third in a Labour/Conservative marginal), Berwickshire, Roxburgh & Selkirk to the Conservatives, Caithness, Sutherland & Easter Ross to Labour, Dunbartonshire East to Labour, Edinburgh West to Labour (with the Conservatives pushing the Liberal Democrats into third place), Fife North East to Labour (which becomes a 3-way Labour/Conservative/Liberal Democrat margianl, and with 4.15% separating Labour and the Liberal Democrats would be Great Britain's closest 3-way marginal), Gordon to Labour (and falling to fourth place as this becomes a 3-way Labour/Conservative/Scottish National Party marginal), Inverness, Nairn, Badenoch & Strathspey to Labour, and Ross, Skye & Lochaber to Labour.