"As every football fan knows, you don't win the league by a good result in February."

Sir Keir Starmer says that despite Labour's victories in the Wellingborough and Kingswood by-elections, "we've got to fight for every vote". pic.twitter.com/Qz2iDv3O1B

— Channel 4 News (@Channel4News) February 16, 2024

'Mid-term by-elections are always difficult for incumbent governments'

Rishi Sunak has insisted the circumstances surrounding the Wellingborough and Kingswood by-elections were 'particularly challenging' after suffering a double defeat to Labour pic.twitter.com/vW1obuT7Pb

— ITV News Politics (@ITVNewsPolitics) February 16, 2024

There have been 21 by elections so far this parliament. What prospects do the results show for the government at the next general election?

Let’s start by leaving aside a) the two SNP defences, as neither involved the Conservatives as the main challenging party, and b) Southend West, due to the special circumstances in which no major party challenged the defending Conservatives. This leaves us with 18 contests.

The swing from Conservatives to the main challenger (Labour in 14, Liberal Democrats in 4) averages 15.6%. Putting this into Electoral Calculus, and assuming a high level of tactical voting between Labour and Lib Dem, gives Labour 322, Con 257, LibDem 32: significant change on the current position, but with Labour just short (by 4 seats) of a majority.

If we look only at Conservative defences – and it’s certain they’ll be playing defence in the General Election, the position looks somewhat worse. Across the 12 Conservative defences this parliament, the swing away from them has averaged 21.7%. That’s nearly half as bad again as the previous figure, albeit with a smaller sample we need to be a bit more cautious about possible errors. On these figures, Electoral Calculus predicts Labour 362, Conservatives 199, LibDems 50. A strong Labour majority, a recovery to pre-coalition numbers for the LibDems, but not total wipeout for the Conservatives.

Just one other warning flag for the Conservatives, again with a caveat about small sample sizes. Where the Conservatives were defending against Labour, the average swing was 10.2% in 2021, 12.8% in 2022, 18.7% in 2023, and 22.5% in 2024. This is not a good trend line.

James Doyle