Amid all the hoopla about Britain leaving the European Union, including the Single Market, one fact has always stood out for me, a bit like a foglight piercing the mists of a grey January morning.

During our 44 years of EU membership, the UK went from being, by its own admission, the Sick Man of Europe, unable to pay our bills, reliant on the goodwill of the International Monetary Fund, to being the fifth-largest economy in the world.

We did this, apparently, in spite of Europe, in spite of the meddling of unelected bureaucrats, in spite of the machinations of the European Court of Justice and in spite of the mountain of red tape allegedly erected between us and customers around the world clamouring to buy our goods.

You’d never have surmised any of this from Theresa May’s leaving speech. 

Leavers like to say that the benefits of being part of Europe might just about have been discernible in the distant days of the dear old Common Market but that everything since has been downhill. Yet, if anything, the change, from grim post-imperial malaise to Wirtschaftswunder accelerated and deepened during the premiership of Tony Blair, whose slogan was that Britain was at the heart of Europe. In more recent days – beyond the immediate euro crisis and the impact of the 2008 recession that affected the entire Western world, America included – Britain’s growth has resumed. Even now, in spite of seven years of self-inflicted austerity, we remain in profit and are continuing to grow.

But, as we Remainers like to point out at every available opportunity, nothing thus far has changed. Given that the Prime Minister has confirmed her intention to initiate a “clean break,” it could be that we will be out sooner than expected. But for now, as I write, Britain is in the same position it was in yesterday and every day for the last 44 years: a full and functioning member of the European Union. So, the economic success of which we boast with all the preening certainty of Mr Toad has not been achieved as a proud and independent nation, dealing freely with the world, but as a member of the largest and most enduringly successful trading block in the world.

Those who say that Europe has outlived its usefulness and is, in any case, in a state of incipient collapse have yet to convince us that David Davis, Boris Johnson and Liam Fox can lead us into an alternative Age of Plenty in which British goods and services become the gold standard of international exchange. It would also help if they would reveal how, operating as capitalism’s evil twin, we could somehow become a combination of Singapore, Luxembourg and the Wild West, in which anything can happen, and probably will.

For these are the alternative vistas thrown up by the Prime Minister’s Great Repeal Speech.

The more prosaic truth is that Brexit, once done and dusted, provides the opportunity, which millions of Brits have certainly demanded, for a demographic reset. Gradually, over a period of, say, five years, many of the Poles and other East European migrants who have toiled in Britain since 2004, contributing greatly to its success, will filter back to Europe, either to their own countries or to Germany. At the same time, those who remain will tend to adopt British traits, as will their children, so that we can then stop talking about them or thinking of them as alien.

Integration is already happening and will continue. It just doesn’t happen overnight.

But while EU migrants will decline in both numbers and “foreignness,” they will in due course be replaced in the workplace by a million or more new arrivals from the ethnic Commonwealth and other parts of the developing world. We know this because British industry has said as much. Companies cannot get enough of foreign workers, who put in longer hours and tend to be better educated and more malleable than their British counterparts. They also have skills that the British proletariat largely abandoned in the Thatcher years. You only have to look at the ethnic background of most new millionaires in Britain to realise that it is immigrants who have done most in the last 50 years to Make Britain Great Again. The Tories know this, as does Nigel Farage, who has often spoken of the need to attract more English-speakers to take the place of the EU mercenaries who make him feel so uncomfortable on trains.

Britain in 2030 is likely, in fact, to look less like it used to in the imaginary days of the 1950s than it does today. And the same people who complained about cultural saturation by East Europeans will no doubt start to complain, and complain bitterly, about the new wave.

But let us not get ahead of ourselves. What we heard on Tuesday from Mrs May, with all its talk of “we’re off, but, hey, we really like you and want to keep you as friends,” is a classic menu without prices.  

She doesn’t know what the economic future holds. She and her colleagues are starting from scratch. It is Year Zero. Having handed England back control of its borders and the right, over a period of years, to negotiate new trade deals, including a grand pact with Brussels, she must now preside over a people demanding policies and interventions that, freed from the dead hand of Europe, will transform the lives of the Just About Managing she keeps banging on about.

Industry, commerce and banking, meanwhile, will be drawing in their breath. What will UK carmakers (all foreign-owned) do once they are taken out of the single market? What about those promises to Nissan and others that they have nothing to worry about over Brexit? What about the City of London, whose hopes of holding on to its EU passport are left dangling on the slender thread of Michel Barnier’s goodwill? What about small businesses trying to sell into Europe who will in future face tariffs and other customs barriers? What about Northern Ireland, which instead of living amicably with the Republic, must now erect and police a land frontier with the EU?  What about British expats, all 2 million of them, who could find their lives made a misery by new arrangements yet to be put in place, including, quite possibly, loss of health cover? 

The PM ticked off each of these issues, but gave no indication of how they would be addressed other than to say she would be strong and constructive. Ending with a threat to adopt the Singapore option if Europe didn’t play ball and with a brief nod to the press (whose questions she artfully dodged), she then strode off into a policy purdah that could last for the next two years. You could almost hear the door slamming behind her.