Momentum, the Labour campaign group dedicated to keeping Corbynism alive, this week demanded that Keir Starmer commit to introducing a proportional voting system should he win election, replacing the current first past the post model for electing MPs.

‘A popular consensus is building across the labour movement for a change to our first past the post electoral system, which has consistently delivered Tory majorities on a minority of the vote and hands disproportionate power to swing voters in marginal constituencies,’ said Gaya Sriskanthan, Momentum’s co-chair. ‘Momentum will join the charge for PR, as part of a broader commitment to deep democratic change and alongside our strategy of building popular support for socialism in our communities.’

Why, of all the things Momentum could campaign for, would they pick changing the voting system? It is because the following logic has formed into a sort of dogma on the left of British politics over the last couple of years: we have a ‘progressive’ majority in this country, but the voting system allows the Tories to win on minority support; if we had a PR system, the splits amongst non-Tory voters would matter less and this ‘progressive’ majority could assert itself at the ballot box. The result, surely, would be permanent centre-left governments.

I worked on the Yes to AV campaign and following that, for the Electoral Reform Society for a few years, so I’ve thought more about this than I really should have. And I can tell you that Momentum and indeed the wider left’s logic here is deeply flawed. In fact, the introduction of a proportional voting system would have almost exactly the opposite effect they seem to think it would.

For a start, PR would be terrible for the Labour party. I don’t think they’d survive two general elections after its introduction, breaking up into several different entities along the way. First past the post is actually the only thing that has held them together over the past decade.

Proportional representation would be terrible for the far left, who would never get enough seats to have any element of their true agenda realised. PR is all about compromise, something they are clearly terrible at.

Momentum and the greater left’s misconceptions about proportional representation go far deeper than all of that, however. Cheerleaders for PR on the left like to take the 2019 general election result and then divvy up the seats proportionally on the basis of each party’s vote share. Anti-Brexit parties would then have got a slightly higher percentage of the vote than the ‘pro-Brexit’ parties. See! If we’d had PR, Brexit wouldn’t have happened, right? Wrong.

One of the features of a proportional voting system is that people vote differently than they would under first past the post. For instance, in the 2019 general election, many pro-Brexit voters could have put the Brexit party as a first choice and Tories second without fear of splitting the right of centre vote and letting Labour get seats. As a pertinent example, look at Hartlepool in 2019 — a large Brexit party showing meant the pro-Brexit vote was split, allowing Labour through the middle. This could never have happened under a PR voting system.

Given the Brexit party were polling at over 20 per cent in the lead up to the election, it isn’t at all fanciful to think that with PR in place, the Brexit party would have done extremely well in the 2019 general election. In fact, had the voting system been proportional, it stands to reason that the most likely government afterwards would have been a Conservative-Brexit party coalition. Hell, we probably would have got a no-deal Brexit if PR had been in place.

Electoral reformers on the left don’t often mention the 2015 general election, when the combined percentage of Tory, Ukip and the two Unionist parties in Northern Ireland was 50.4 per cent of the vote. It seems this ‘progressive’ majority doesn’t even always exist under first past the post. Now imagine for a moment how well Ukip would have done in 2015 under PR given they got almost 13 per cent when they were mostly a wasted vote. How many more voters would have backed Farage if they were able to dispense with tactical voting?

If you are in favour of a proportional system of voting because you think that it is a fairer means of deciding who runs the country, fine — just don’t kid yourself into thinking that it will benefit the centre-left in any meaningful sense. It is much more likely to do the precise opposite. In fact, a PR voting system for the House of Commons could strengthen the centre-right enough to keep them in government for the rest of the century.

There we have it: Jeremy Corbyn’s activist army, campaigning for something that could destroy the Labour party and strengthen the right’s hold on power. Although come to think of it, Momentum have done plenty of both of those things already, so why break form now, I suppose.