Richmond result shows the risks for Theresa May in calling a snap election

Political pundits, including luminaries such as Michael Portillo, expect the prime minister to stroll to a general election win due to the low approval ratings of Labour’s Jeremy Corbyn.

The likelihood is that they are right, and that Mrs May would win an increased majority. By-elections are notorious forums for protest votes – the Conservatives lost one safe seat after another in the late 1980s and early 90s before going on to win a ‘surprise’ re-election in 1992.

But even so, there are big imponderables for the Conservative Party leader.

Some people thought that the catastrophic performance of the Liberal Democrats in the 2015 general election – a paltry 8% of the vote – was the end of the party. But having punished them for going into the coalition with the Tories, natural Lib Dem voters might return en masse. No section of the electorate is more pro EU than them. They might be joined by moderate Tories who resent Brexit.

The threat from Ukip is also unknowable. Nigel Farage is a hard act to follow but it might be that Paul Nuttall resonates just as forcefully as he did with ex Labour voters.

Labour itself might do better than expected. Mr Corbyn is seen as too extreme but the fact that he took the Labour leadership by surprise, and then held it despite the overwhelming opposition of his MPs, shows how unpredictable voting behaviour is now.

There is a serious view now that Bernie Sanders might have beaten Donald Trump in a head-to-head presidential race. A year ago no serious pundit entertained the prospect of man who once labelled himself socialist becoming president of the United States, but the same pundits wrote off Mr Trump getting the Republican Party nomination, let alone more. They did not foresee Mr Sanders almost defeating Hillary Clinton in the contest for the Democratic Party ticket.

A Labour revival in Scotland is a further risk to the Tories. It seems unlikely just now but polling this week did find a slight drop in Scottish nationalism since the 2014 independence referendum. It might be that the Scottish National Party has overplayed its hand and that Labour will begin to reclaim some seats in one of its former heartlands.

Then there is the possibility of agreed anti-Brexit candidates toppling enough Tories to deprive Mrs May her majority. Such candidates could emerge suddenly, perhaps after a social media campaign, regardless of the wishes of party leaderships.

The Conservatives could respond with single pro-Brexit candidates in a loose pact with Ukip, but that would damage Mrs May’s moderate credentials and displease her party’s Remain wing.

Fuelling the unpredictablity is Britain’s first-past-the-post (FPTP) voting system. It is a constitutional outrage that Ukip’s four million votes at the last general election resulted in only one MP.

Parties that do well out of FPTP support it, but increasingly splintered voting patterns are throwing up some ridiculous outcomes.

Soon supporters of FPTP might encounter results they dislike so much that they find their support for FPTP tested, such as Labour last year in Scotland which got 24% of the vote but 1% of the MPs. The Ulster Unionists won 11 out of then 17 Northern Ireland MPs in 1983. By 2010 it had none.

The combination of FPTP and current voter volatility could put Mr Corbyn in Downing Street, at the helm of a Lib-Lab pact, although such a result is still unlikely.

I was once fond of the tradition and clarity of FPTP, and the atmosphere it creates, but some years ago concluded that the UK needed the Additional Vote (AV) system – the one that was conclusively rejected by the British public in the 2011 referendum after a disastrous pro AV campaign.

AV maintains the link between MP and constituent in single member seats, but would put a stop to the rise in outcome anomalies (ie Ukip shortfall) in recent elections.

Such anomalies will probably work to Mrs May’s advantage next time but might – if like Zac Goldsmith she calls an unnecessary election – end her career.

• DUP IS WELL PLACED ELECTORALLY

Perhaps the UK party best placed electorally now is the DUP. Sam McBride, opposite, explains how the Richmond result has increased their influence at Westminster, which was already huge, as this column noted in September. The maths is agonisingly tight for Theresa May, and holding a snap general election in a bid go increase her majority would, as explained left, be a perilous move. But the DUP is also one of the few incumbent political parties in the western world that is benefitting from the anti incumbency mood that has swept the West. Earlier this year I thought that mood would cost them seats. But perhaps they are seen as anti incumbent (ie Sinn Fein incumbent). They also stand out against a lot of the things that are annoying voters, particularly blue collar voters, such as anti elitism and cultural anxiety.

• Ben Lowry (@BenLowry2) is News Letter deputy editor

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