In any other world there would be national soul searching. Britain’s economic growth rate over the past 12 months is half its average over the previous 25 years – and set to deteriorate further. Investment is stagnating. Mortgage approvals in March slumped by almost 21%. Car output for the domestic market has dropped in the same month by 13%, for export by 12%. These are dramatic numbers.

To drive the point home, on Friday we learned that in the first three months of the year, Britain grew at its slowest rate for five years. One comforting explanation is that the “beast from the east” hit construction. But dig a little deeper, and the cold snap also prompted a surge in demand for electricity and gas. As the Office for National Statistics observed, the weather alone explains little of the setback.

Output from manufacturing and services was just idling in January and February before an ominous gathering slide in many areas in March. This should be sounding alarm bells everywhere – it is plainly why Bank of England governor Mark Carney signalled that an interest rate rise slated for next month may be deferred, and why the pound was sold so aggressively after the news. If there had not been a world boom over the last two years, it is clear that the UK would be hovering on the brink of a recession; indeed, as the world economy falters in the months ahead, there is now a real prospect of just that.

If you are a passionate Brexiter, this is just some frictional difficulty before the British economy moves to the sunlit uplands, riding the boom in the fast-growing economies of Asia as it does trade deals aplenty. After all, Remoaners don’t draw attention to unemployment falling to a 40-year low, the companies who threatened to leave instead of committing to the UK, and the ongoing strength of our high-technology sectors.

It’s true that unemployment is hearteningly low. But unemployment is what economists call a lagging indicator – the last statistic to turn sour in any recession. It reflects what economic conditions were twelve months ago. More importantly, it is no longer the sole proxy for labour market health. Since the financial crisis, real wages have fallen by a stunning 10%. Over the last generation, the UK has become the global leader in creating low-paid, low-skill, casualised work. In any three-year period, such is the churn in the labour market that a third of the workforce find themselves in poverty. Without either strong trade unions or a burgeoning knowledge economy, the condition of working life is one of profound hardship and stress.

Everyone, outside the closed world of the Brexit advocates, knows that vandalising our hi-tech sector is supreme folly

Is there good news to indicate where new growth might originate? Very little. As for hi-tech sectors, Britain had real hopes of growing a £40bn space industry by 2030 – of which a cornerstone was more than our fair share in the great EU space projects Galileo and Copernicus. Now we are to be excluded from Galileo, and in particular the encryption technologies that drive the highly effective system for moving government data securely via the new generation of Galileo satellites. It is a tragic loss.

The hits keep coming. The EU used its collective muscle to negotiate an even-handed open skies policy with the US; outside the EU, the US is insisting on a deal that hits British airlines very hard. Who should be surprised? British scientific research was expecting to win £10bn more than the UK government contributed to the EU science budget between 2020 and 2027. That prospect is dead, too. Nor can there be any certainty about what Britain’s trade relationships will be in future.

At present, Britain is the linchpin of the world’s greatest free trade area: the 27 member states of the EU, another 31 countries with whom free trade agreements are signed and operational, and another 30 with provisional deals about to be put in place. This global EU is the citadel and heart of the world’s free trading system, setting standards, from the production of chemicals to the use of data, that the rest of the world follows. There is zero chance that Britain can reproduce this on its own. Everyone, outside the closed world of the Brexit advocates, knows that rupturing these relationships and vandalising our hi-tech sector is supreme folly.

Thus the business world is, at best, watching and waiting; at worst, actively taking measures to protect itself by moving activity to mainland Europe. Figures released by the OECD on Friday show inward investment into Britain slumped by $181bn over the last year; outward investment has boomed by $120bn. This is one of the biggest one-year turnarounds by any country ever recorded. But it is scarcely reported.

Put all this together and Britain faces the gravest economic crisis since the war. The growth model on which we have relied – inward investment booming because Britain is the heart of the world’s greatest free-trade area, married to emergent strengths in high technology dependent on access to that market – is being shattered.

There is nothing to put in its place – but our vastly overpriced housing market depends on it continuing. If it does not, it could have the severest of consequences. Faced with this challenge, our national debate is disgracefully frivolous. The Treasury’s pre-referendum warnings about Brexit are suddenly looking more prescient. Those who connived in this debacle will be damned by future generations. Our country needs and deserves better.

• Will Hutton is an Observer columnist