Why Lib Dems’ by-election win is unlikely to spark change

Start with history. Chesham and Amersham was the 24th Conservative seat since the Second World War to be lost to the Lib Dems or their predecessor parties (Liberals or SDP). Of the previous 23, just nine by-election winners held their seat at the following election. Thirteen lost to the Tories, one to Labour. Of the nine that stayed Liberal, SDP or Lib Dem, seven saw their by-election majorities reduced, often sharply.

True, the Lib Dem majority last week, 21.1%, was bigger than in most by-election triumphs. Just three exceeded it. But of those three, two (Sutton and Cheam, 1972; Christchurch, 1993) reverted to the Conservatives at the following election. All in all, history suggests that Sarah Green has a less than evens chance of holding her seat next time.

That said, as those financial advertisements say, past performance is no guarantee of future results. Could the Lib Dems defy the odds this time and shatter the Tories’ blue wall? Here are two reasons that have been advanced for saying they might:

First, past Tory by-election calamities have almost always happened when their prime minister has been floundering. This time, opinion polls show Boris Johnson and his party riding high. It’s one reason why Chesham and Amersham came as such a surprise. This is partly because many voters were concerned with two specific issues: HS2 and the proposed new planning rules for new homes. Voters could give vent to their anger, safe in the knowledge that the Conservatives would still have a big majority in Westminster. That suggests a mid-term protest that will subside at the next election.

The other reason could be more enduring. The character of Conservative support is changing. As we saw in Hartlepool, and may see next week in Batley and Spen, the Tories are gaining ground in former Labour strongholds, but slipping back in sections of their own heartlands. Chesham and Amersham was an example of this, even before last week. In 2015, the Conservatives won 37% of the Britain-wide vote, and 59% in Chesham and Amersham. In the general election 18 months ago, the figures were: national: 45% (up 8 points on four years earlier), Chesham and Amersham 55% (down 4).

That contrast – national vote up, local vote down – was typical of a particular type of constituency: prosperous southern areas that traditionally produced large Tory majorities but voted Remain in the Brexit referendum. (Chesham and Amersham voted Remain by 55-45% Leave.) That pattern was visible in last month’s local elections, with the Lib Dems and Greens capturing a raft of council seats in these very areas.

Could this portend trouble for the Conservatives at the next general election? To make an obvious arithmetical point, it would make no difference to Johnson’s overall majority if Tory losses in the well-heeled south are offset by further gains in the Red Wall north and Midlands. Here’s the rub: there are more Labour MPs vulnerable to the Tories than Tory MPs vulnerable to the Lib Dems.

These are the key figures. (Boundary changes will make some difference, but the broad picture is likely to remain much the same.) At the last election, the Lib Dems came second to the Conservatives in 81 seats. However, 43 of them voted Leave in the Brexit referendum, and almost all of these have substantial Tory majorities. That leaves 38 Remain-voting seats where the Lib Dems are the challengers. Eleven of these have Tory majorities of more than 30%. I doubt whether the Lib Dems will spend scarce campaigning resources on these.

If one limits the targets to Remain seats where the Lib Dems are within 20%, and so need a swing of less than 10%, the number falls to 17. Admittedly winning these would mean capturing some Tory scalps, such as Dominic Raab and John Redwood. However the numbers look modest. The party would be doing well to gain a dozen Tory seats. This would dent the Tories’ overall majority, but not wipe it out. In contrast, a 10% swing to the Tories in Labour-held seats would give Johnson as many as 93 new MPs. Even a swing of just 3% would cost Labour 26 seats.

For the next election to produce a change of government, Labour must do the heavy lifting. It must hold all its current seats and gain more than 120 to win an overall majority, and around 80 to become the largest party.

The good news for Labour is that it won’t need quite as many to remove Johnson from Downing Street. The Conservatives will need at least 310 MPs (out of 650), and probably more, to remain in office. For example, suppose there are 310 Conservatives facing 260 Labour, 40 Scottish Nationalists, 20 Lib Dems and eight other anti-Tories (Green, Plaid Cymru and Northern Ireland’s SDLP and Alliance). These 328 MPs would outnumber the Tories by 18 in the new House of Commons.

Even if the Democratic Unionists agree to side with the Tories, as they did in 2017, Johnson would not have enough MPs. If Labour can strike some kind of deal with the SNP and Lib Dems in particular, Sir Keir Starmer could become prime minister, even if his party has 50 fewer MPs than the Conservatives.

Labour, of course, has its own troubles. Getting to 260 won’t be easy. It must find some way to re-assemble the coalition that delivered past victories, most notably under Tony Blair: traditional working class voters joining forces with socially liberal middle class graduates. The Chesham and Amersham result opens up a handful of exotic Lib Dem possibilities in the well-heeled south; but there is no chance of a non-Tory government without a big Labour revival in the north and Midlands.

Chesham and Amersham was certainly dramatic. However, what happens next week in Batley and Spen will be more significant.

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