Borrowing to pay for the largest tax cuts in 50 years was something the bond market simply could not swallow.
While Kwarteng was reportedly celebrating at a pub after his Budget speech, the pound was plunging to its lowest level since 1985.
In the following days, chaos broke out on the markets. At times there were no buyers at all for long-term gilts, something unheard of even during the worst days of the GFC.
Banks responded to the volatility by withdrawing 40 per cent of their mortgage products and sharply increasing rates on those that remained.
Before long the chain reaction was threatening pension funds. That was enough for the Bank of England to step in with an emergency intervention to shore up the markets.
By Tuesday, Kwarteng was forced into a humiliating U-turn on the top tax rate. While that calmed the markets a little, it did nothing to arrest the Government's plummeting poll ratings.
Labour's lead on the Tories now averages 25 per cent. And crucially, on economic management, the Conservatives now trail Labour by 19 points.
Given all the commotion, it didn't take long for New Zealand's political seismographs to start twitching.
With plans of their own to abolish the top tax rate, National came under immediate pressure to explain how this would be paid for.
Sensing vulnerability, Grant Robertson has been happily whacking the tax cut pinata and accusing National of living in a "fiscal Bermuda Triangle".
But beyond the debate on their tax plans, there is a wider problem for National and its centre-right friends worldwide.
The decades-old political wisdom that parties on the right are better at managing the economy is starting to crack.
By any objective measure, Labour has managed the country's books pretty well over the past 25 years.
As Finance Minister, Sir Michael Cullen delivered nine years of surpluses. He reduced debt, created the Super Fund and Kiwisaver, and maintained New Zealand's AA+ credit rating.
His successor, Grant Robertson, has now delivered five successful Budgets guided by Labour's Budget Responsibility Rules.
Treasury's release of the latest Crown accounts on Wednesday painted a picture of a finance minister doing a very good job in the circumstances.
The country's books are healthy overall, with company profits up, government spending under control, and a deficit that is half as large as forecast.
Perhaps all this shouldn't come as a big surprise. Even in opposition Robertson released a fully costed alternative government budget, verified by BERL.
Paradoxically, maybe it's the accusations of not being good economic managers that make Labour finance ministers so diligent.
Ironically this could be the same reason why at times, centre-right parties appear to slack off.
From the UK to Australia to the US, these parties are guilty of taking their economic credibility for granted.
These days many right-wing politicians seem more interested in starting pointless culture wars and obsessing over society becoming too "woke" than focusing on the economy.
Recent events in the UK should therefore serve as a warning.
When it comes to economic policy, the market doesn't care what party you're from. It does care if your plans don't add up.
As Bill Clinton said when asked for the secret to producing a Budget surplus: "arithmetic".
Andrew Kirton was Labour's General Secretary from 2016-2018. He now works in government relations for transtasman firm Anacta Consulting. He is married to a Labour MP.
