“In gambling,” George Bernard Shaw once said, “the many must lose in order that the few may win”. The old Fabian could just as easily have been talking about British elections. Last week was a disaster for the Labour Party and everyone who depends on it. With a Conservative majority and a Prime Minister free to decide how we leave the EU, we seem to be on the brink of the biggest reshaping of our society in decades. Forget Theresa May – it’s Boris Johnson who’s set to be the real Margaret Thatcher 2.0.

But it’s the many who lost last Thursday. A clear majority of voters backed parties to the left of the Conservatives. The Tories may have won 56% of the seats, but they received less than 44% of the votes. This outcome is only possible due to the UK’s undemocratic first-past-the-post (FPTP) voting system. And the Labour Party is the only socialist or social democratic party in any major developed country to support such a system.

To be clear, this is a policy decided at the top – not by the grassroots. Polling conducted for Make Votes Matter last week revealed that three-quarters of Labour members believe the party should back proportional representation (PR). Just 12% said it should not – a small minority that unfortunately includes some of the most influential Labour voices.

As with playing roulette, there would appear to be pros and cons to supporting FPTP. The pros are that you may win a prize far exceeding what you could win in a less random game: whether it’s a lot of money, or whether it’s a Labour majority government on a minority of the vote. The cons are that you may end up losing far more than you can afford to lose.

And, as in roulette, the apparent balance of pros and cons is an illusion. There is no balance. The casino has a winning edge and – on a long enough timeline – the house always wins. Labour’s historical support for FPTP has been based on a gambler’s logic, applied on a momentous scale.

FPTP – along with other winner-takes-all voting systems – is widely acknowledged by political scientists to have “a pronounced right-wing bias”. Countries with such voting systems have had significantly more right-wing governments than those with proportional systems – and they’re expected to continue to do so.

This isn’t just a run of bad luck. In a book published earlier this year, Professor Jonathan Rodden revealed that since World War II every single developed country with a winner-takes-all voting system has on average had a parliament that is more right wing than its voters. In almost every case, their cabinets have been even further to the right. Two-thirds of all governments formed in these countries have been right wing, despite left-wing parties winning slightly more votes in almost every case.

This is partly due to demographic geography. For historical and cultural reasons, progressive voters across the world are over-concentrated in urban areas. This means major left-wing parties pile up huge mountains of votes in cities, while major right-wing parties have a relatively even distribution of votes across nations. Under FPTP, the latter is much more efficient. Labour now holds about three-quarters of the 30 safest seats. In the last parliament, Labour held 29 of them. These are the seats in which we get most the votes, but they’re also the seats in which votes for winning candidates have the least value.

Additionally, PR allows for progressive parties to stand for election independently and then work together in coalition. With FPTP, the only alternative to a right-wing government is usually for all progressive voters to rally behind a single left-wing party. This happens only very rarely, leading to vote splitting and right-wing government on a minority of the vote.

The UK is no exception to this logic. In 19 of the last 20 general elections, most people have voted for parties to the left of the Conservatives, yet the Tories have been in power for 63% of this time. By 2024 this is set to rise to two-thirds of the time – without the Tories once securing a majority of the votes. So last Thursday’s result – a progressive majority of voters but a Conservative majority of MPs – was really no surprise. It is actually the most common outcome under FPTP.

Make no mistake, Labour did badly last week. There is no voting system that would have turned this defeat into a triumph. Winning only 32% of the votes shows that something went very wrong, and I’ll leave others to debate where the blame lies. But if Thursday’s votes had been counted under a proportional system, Labour would now be regrouping in a parliament that is mostly to the left of the Tories, rather than one that is mostly to the right of voters.

The failure of past Labour governments to get rid of FPTP has harmed not only the party but those who depend on us. Long-term Conservative hegemony has made the UK one of the most unequal societies in the developed world, in contrast to the most equal countries which all achieved what they have through PR.

It was rightly pointed out during the election that Labour’s manifesto would simply have levelled Britain’s public spending with many of our European neighbours. It may now be 2024 before there’s another chance to close this gap. In the meantime we fall further behind – and lifetimes continue to pass by without the adequate public services that people both need and voted for.

Dazzled by the prospect of majority governments, the Labour machine has allowed itself to gamble on a system that is objectively stacked against it. The manifesto stubbornly refused to even mention the voting system, meaning we’d be set to continue gambling in the future even if a Labour government had been elected last week.

It’s time for an intervention – and it needs to be led by those who care the most: members, affiliates and allies. Those who want a society ‘for the many’ must no longer tolerate a rigged system. Members of most affiliated unions have a month or so to send motions to their 2020 conferences. Labour members can invite speakers to their CLPs. We must all make this issue impossible to ignore during the leadership debates, and look ahead to the autumn conference. With Labour committed to electoral reform, the party can get to work seeking re-election, transforming society and removing the right-wing bias that has dominated seven decades of British politics.