The by-election result in Denton and Gorton is seismic, and will rock Westminster to its core; put simply, never before have the mainstream political parties looked more out of touch with the rest of the country.
It presents questions principally to the Labour party and its leader, Sir Keir Starmer - who, with some understatement, called the result "very disappointing" - but also to the Tories, Liberal Democrats and Reform UK too.
It was a clear win for the Greens, with a strong showing by Reform UK, both making huge gains on their showing at the 2024 general election.
It was the Greens' first-ever by-election win. Labour's vote halved, while the Conservatives and Liberal Democrats were barely ahead of the Official Monster Raving Loony Party's candidate, Sir Oink A-Lot.
Truly, the middle ground of British politics, the space dominated by the Tories, Labour and the LibDems in Parliament for decades, has disappeared.
Never before have Westminster's MPs looked more out of touch with the rest of the country. And the threat to the three main parties looks increasingly existential.
I am writing this newsletter on Friday morning from a community centre in Denton and Gorton, where the new Green MP Hannah Spencer - a plumber by trade - has just delivered a five-minute victory speech, the morning after the by-election.
Spencer mentioned the cost of living crisis, spiralling bills, the problems of finding an affordable place to live, the crisis in Gaza; the environment was referred to just once. It was a speech any left-wing Labour MP could have given. No wonder.
The Greens are now gunning for Labour's core vote. Spencer concluded: "We are not here to be disappointed by Labour - we are here to replace them."
Those words will send chills through the 40 Labour MPs where the Greens came second in the 2024 general election, who until now have not had to worry, like their Labour colleagues, feeling the heat from Nigel Farage's resurgent Reform UK.
Greens' leader Zac Polanski seemed like a shell-shocked lottery winner. "This was our 127th target seat," he said in disbelief.
The era of five-party politics has emphatically arrived. This will rock Westminster to its core
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His party has fought 87 by-elections and never won more than 10 per cent of the vote. Last night they won over 40 per cent.Of course, all of the usual caveats apply about the result of a mid-term by-election - that this was a protest vote; that people might behave differently at a general election where their votes will influence which party forms the next government.
But, still. Polanski now sees his party winning 30 MPs at the next election as a baseline for what they might achieve. And why not? The Greens' membership in England and Wales has jumped from 60,000 last September to nearly 200,000 in just six months.
The Greens will face increasingly scrutiny of their policies - notably legalising hard drugs and leaving Nato - but I can't see how these concerns will damage their standing, in the same way that Reform has shrugged off concerns about some of its policies.
These are both, to an extent, "vibes" parties where the details of what they would do in government are still being formed.
Reform UK can be pleased with its showing in second place in a seat like Gorton and Denton, although Polanski told me Nigel Farage was showing "sour grapes" after the Reform leader said last night was a "victory for sectarian voting and cheating".In truth, the seat was always going to be a battle between Labour and the Greens about who could stop Farage - and the Greens won.
This presents huge problems for Labour - should the party now lurch to the Left to combat the Greens or keep trying to face down Reform UK? No wonder potential leadership challenger Angela Rayner called the result a "wake-up call" for the party.
And it presents a big concern personally, Sir Keir Starmer, who campaigned here earlier this week and who blocked Greater Manchester Mayor Andy Burnham from standing in the by-election, saying he was worried that it would overstretch the party's resources.
Polanski and Spencer said they came to the conclusion during the campaign that Burnham would not have won, such is the disaffection here for the Labour Government.
Still, mark today's date as the Gorton and Denton by-election will go down as a landmark in British politics, when the era of five-party politics now finally and emphatically arrived.
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