US Congressional primaries don’t usually make international news. While the world habitually follows the twists and turns of the presidency, legislators on Capitol Hill are only known to the most avid of politicos on the other side of the Atlantic.

But this June things changed. In New York’s 14th congressional district, a 28-year-old community organiser and part-time bartender defeated one of the country’s most senior politicians and became the Democratic candidate in this year’s Congressional elections. It was America’s biggest political upset since the election of Donald Trump, and the world was introduced to Alexandria Ocasio-Cortez.

Ocasio-Cortez’s primary win caught the attention of progressives across the world for many reasons. A young woman of Puerto Rican heritage, Ocasio-Cortez will be the first person of colour to represent a district in which more than 80% of the population are non-white. Outspent by a factor of 15 by her corporate-backed incumbent, her campaign drew on the movement-oriented strategies that have characterised political upsets on both sides of the Atlantic. But most importantly, Ocasio-Cortez demonstrated the potential for an American progressive to launch a vibrant, radical and winning alternative to both the reactionary populism of Trump and the failed centrist politics of Hilary Clinton’s presidential campaign.

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Ocasio-Cortez embodies the movement-led, popular politics Momentum was born to promote in the UK. And with Labour surging to more than half a million members, there is no doubt we have many of our own like Ocasio-Cortez just waiting for their chance. But despite the wealth of talent in our movement, and the potential to enliven our parliamentary benches with fresh energy and passion, a new generation of Labour MPs are being shut out by Labour’s restrictive, outdated rulebook.

Unlike the primary system that operates in the US, it is notoriously difficult to challenge a sitting Labour MP. Instead of being able to run in an open contest on a positive and propositional platform as Ocasio-Cortez did, Labour has a built-in mechanism that forces local party members to mount a negative campaign against their sitting MP just to instigate a race.

Play Video 3:47 'This is the beginning': Alexandria Ocasio-Cortez's victory speech – video

Despite obsessional reporting in some parts of the press, most local Labour members are far more interested in fighting the Tories than one another. Such a divisive selections process puts off many would-be candidates, and has left Labour with only a handful of open contests in Labour-held seats in nearly 30 years. Ocasio-Cortez would never have been elected if she had been subject to Labour’s restrictive rulebook, and as things stand many of our most talented members will never get a shot at becoming an MP.

The lack of democracy is striking, and we’re hoping the Labour party conference will ditch this outdated practice. We want to see a process that gives a fair chance to all candidates and improves the atmosphere in local parties by doing away with the negative, divisive stage of campaigning and making it an open contest from the start. This means, in all constituencies, local members and the sitting MP would be free to compete for the Labour party’s backing at the general election – and able to run positive, vibrant campaigns talking about the issues voters actually care about in order to become the Labour candidate.

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Not only will this open the door to a new generation of MPs, it will bring current Labour MPs closer to the members, help them stay in tune with the needs of their constituencies and ensure the deep, collective knowledge of our half a million members – who live and work in every kind of community across Britain – is properly utilised.

Of course, calls of “purge” will emanate from the usual minority within the party, and will be seized upon by a certain section of the press. But instead of crying foul, those who back the status quo should actually defend it and present a positive case for the current rules. Ours is a party on the verge of government, and we must foster a culture where the big issues – including workings of our party – are up for discussion and open to change.

Without an open door to would-be MPs and a chance for members to have their say the enthusiasm and energy will quickly ebb away. More democracy rather than less is how we will empower our half a million members, build a social movement-style party and win the next election. More democracy is also, incidentally, a core Labour value, with commitments to democratise the economy and society at the heart of our plan for government. As a party, it might be time to begin practising what we preach.

• Laura Parker is Momentum’s national coordinator