Just after the 2015 election the Fabian Society published The Mountain to Climb, a short research paper which demonstrated just how hard it will be for Labour to win a majority at the next election, once new constituency boundaries are...

Just after the 2015 election the Fabian Society published The Mountain to Climb, a short research paper which demonstrated just how hard it will be for Labour to win a majority at the next election, once new constituency boundaries are in place. Yesterday draft boundaries for England and Wales were published for consultation, enabling us to start to update our 2015 analysis.

The top line is this: to win a majority Labour will need to win 97 seats more than it would notionally begin with, if the boundaries proposed yesterday are used in a general election. To win all these seats in England and Wales alone implies a 10 per cent swing towards Labour in its marginal seats outside Scotland.

Of course, a lot could still happen, and probably will. These are only draft boundaries and some will be revised following submissions from the political parties. The whole process is highly controversial, so there is a chance it could be delayed again. And there’s always the possibility of an election taking place before these boundaries are in place. But as of today these plans are the best we have to go on.

Anthony Wells of YouGov and UK Polling Report has produced estimates of the 2015 vote for each party in these proposed constituencies. Everything that follows is based on these projections – so a big credit to him. On his website he discusses the caveats associated with projecting the 2015 results of seats that did not exist at the time (eg different boundaries would have resulted in different voting patterns). But nonetheless the figures give a strong indication of the challenge Labour faces.

Proposed seats Labour would need to win

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Labour’s mountain to climb

• To win an absolute majority – 301 out of 600 seats – Labour will need to win 97 seats. The party will (notionally) hold 203 seats in England and Wales, and we’ve assumed for the time being that it also continues to hold one in Scotland (the proposals for Scotland are not yet published).

• We can’t yet say how hard it will be to win a majority on the basis of a GB-wide uniform swing, because we don’t know how competitive the SNP-Labour marginals will be. But we can now assess the scale of the challenge, were Labour to make no gains in Scotland.

• To win a majority by making gains in England and Wales only, Labour would need a swing in the marginal seats of 9.8 per cent. The winning line is the redrawn Amber Valley constituency, which has a notional majority of around 10,500.*

• Assuming a uniform national swing across England and Wales, this implies that the Labour vote in the two countries would need to rise from around 32 per cent in 2015 to almost 42 per cent next time.

• This is actually a slightly smaller swing than we said might be required in The Mountain to Climb, based on academic analysis of the previous, aborted boundary review. The outcome of these boundary proposals could have been even worse for Labour.

Staging posts

Winning 97 seats would be extremely challenging for Labour under any circumstances, and current polls suggest the party is on course to lose not gain seats at the next election. So it is worth identifying some intermediate targets. The political consequences of achieving these staging posts may not be desirable for the Labour party, but here we’re just presenting the maths:

• Depriving the Conservatives of a majority would require other parties to take 22 seats from the Tories (we assume the party retains a notional lead in its one Scottish seat). Of the Tories’ 22 most marginal seats in England and Wales, Labour is in second place in 18. Labour’s 18th Tory target seat (Waveney) could be won with a swing of 2.3 per cent – so a swing of this scale might be viewed as the bare minimum Labour should be seeking. In practice the Tories would probably be able to rely on Ulster Unionist support in this situation.

• A majority for a centre-left alliance of Labour, SNP, Lib Dems, Plaid Cymru, SDLP and Green could be achieved if those parties gained 37 seats (but not from each other). For Labour to win all these seats alone would require a swing of 4.4 per cent (to take Erith & Crayford).

• A majority for a Labour-SNP alliance could be achieved if the two parties gained 47 seats (but not from each other). The SNP can only gain a maximum of two. For Labour to gain all 47 seats would require a swing in its English and Welsh marginal of 5.1 per cent (to take Chelmsley Wood and Solihull North).

* In haste, I said on Twitter that the winning line was Basingstoke – a maths error, for which apologies.