A possible early general election: most likely gains for each party

Lately, it has been predicted that there will be an early general election this autumn, which is likely to be triggered by a vote of no confidence against Boris Johnson, although this is not guaranteed to succeed and since the Conservatives still have a working majority of one, there will need to be rebellion by a few Conservative MPs for it to succeed. Claims that it will be held on 1st November, the day after Britain is due to leave the European Union, are spurious not only due to the timing being unworkable in practice but also because general elections in Britain are always held on Thursdays; 1st November 2019 is a Friday.

With the vote likely to be more fragmented than ever before in such a scenario, and with the spate of defections, making plausible predictions is very difficult. Nevertheless, with the Remain/Leave divide remaining the strongest factor, and taking into account the effects of the Change UK split and subsequent developments, I can list what seats each party would gain in such an early general election if it happened this year (comparisons are with 2017 general election):

Labour gain from Conservative (31):

Worthing East & Shoreham, Southport, Southampton Itchen, Hastings & Rye, Pendle, Morecambe & Lunesdale, Camborne & Redruth, Harrow East, Chingford & Woodford Green, Reading West, Milton Keynes North, Milton Keynes South, Vale of Glamorgan, Preseli Pembrokeshire, Clwyd West, Aberconwy, Carmarthen West & South Pembrokeshire, Broxtowe, Norwich North, Watford, Colchester, Calder Valley, Scarborough & Whitby, Shipley, Northampton North, Northampton South, Chipping Barnet, Wimbledon, Harrow East, Putney, Wycombe.

Liberal Democrat gain from Conservative (11):

Cheltenham, Richmond Park, Guildford, Cheadle, Hazel Grove, Lewes, Brecon & Radnorshire (gained via by-election earlier this month), St Ives, Wells, St Albans, Winchester.

Green gain from Conservative (1):

Isle of Wight.

SNP gain from Conservative (10):

All Scottish Conservative seats except Aberdeenshire West & Kincardine, Berwickshire, Roxburgh & Selkirk and Dumfriesshire, Clydesdale & Tweeddale (10 gains in total)

Brexit gain from Conservative (2):

Mansfield, Thurrock.

Independent gain from Conservative (1):

East Devon.

Liberal Democrat gain from Labour (3):

Cambridge, Leeds North West, Sheffield Hallam.

Conservative gain from Labour (5):

Newcastle-under-Lyme, Dudley North, Barrow-in-Furness, Bishop Auckland, Penistone & Stocksbridge.

SNP gain from Labour (6):

All Scottish Labour seats except Edinburgh South (6 gains in total).

Ashfield Independents gain from Labour (1):

Ashfield.

Liberal Democrat gain from SNP (1):

North East Fife. 

Too close to call (17):
Ceredigion, Shrewsbury & Atcham, Telford, Bolton West, Derby North, Crewe & Nantwich, North Devon, Great Grimsby, Rochford & Southend East, Rushcliffe, Rother Valley, Gloucester, Filton & Bradley Stoke, Cities of London & Westminster, Morley & Outwood, South Cambridgeshire, Streatham, Totnes.

In a considerable number of these predictions constituency-specific circumstances have been accounted for significantly. Neither Labour nor the Conservatives are likely to win a majority at present given recent opinion polls, even with the Brexit Party waning since Boris Johnson became Prime Minister. The Conservatives' current Brexit stance under Boris Johnson will mainly seal off many marginal seats they already hold, and with the possible exceptions of Crewe & Nantwich and Derby North a desire for a no-deal Brexit will prevent them gaining any of the seats they lost to Labour in 2017; in most of them a strong Remain vote was a key factor. Meanwhile, Jeremy Corbyn's calls for a second referendum made earlier this year will not endear Labour to swing voters, so the rise of the Liberal Democrats, Greens, and Brexit Party is what is most likely to decide the outcome of many bellwether seats and safe seats that have become marginal as a result of demographic change and the correlating Remain/Leave divide.