Expat Brits – the ones who live full-time in Spain or France, or elsewhere in Europe – number some 1.2 million, equivalent to the combined populations of Manchester and Leeds. Another million or so Brits own homes in in the EU, including many who plan to retire there. Only a small proportion of the full-time residents have jobs. The rest are mainly pensioners who live in homes they bought and renovated years ago that are now worth, on average, no more than €100,000 (£90,000).

At the same time, an estimated three million non-UK EU citizens live in Britain, most of them in England. The great majority are either employed or their dependants. Typically, they are under 40, pay taxes and live in rented accommodation. By any measure, they have made a significant contribution to their adopted country’s economic development over the last ten years. 

If the May Government fails to reach a deal with Brussels under which both sets of expatriates are permitted to remain in their host countries, the result will be a European version of the chaos that followed the partition of India in 1947. Literally millions of people will be displaced.

In Britain, industry will suffer a labour shortage from which it will take years to recover. Business leaders have said over and over again that without the input of EU immigrants – large numbers of whom are far ahead of their UK counterparts in terms of education, energy and skills – their hopes of achieving growth in the coming decade will be dealt a serious, perhaps fatal, blow.

Immigrants tend to work harder, with a greater sense of purpose, than their native colleagues. They have to. Not only are they under constant scrutiny, they are also precisely the type of on-your-bike go-getters whose Tebbit-style determination to make a better life for themselves has given a much-needed boost to Britain’s jaded workforce.

By contrast, in rural France, where I live for nine months of the year, your typical Brits are retirees. Most have planned their futures sensibly. Along the way, they have done much to ensure the survival of France’s much-vaunted rural patrimony. Others live a hand-to-mouth existence, the good life they had imagined forever out of reach. But only one in four, I would say, could reasonably afford to return home. House prices in the UK have risen well beyond their means. In my case, the house in London my wife and  I sold for £305,000 in 2001 was subsequently broken into flats, one of which went last year for £535,000. Property values in rural France over the same period have fallen some 25 per cent and are likely to fall again if the departure of the Brits leads to a glut in the market.

Such considerations used not to matter, except as a topic of pub conversation. British to the core, our would-be lotus-eaters (few of whom think of themselves as immigrants) quietly enjoy their new lives, arousing little or no resentment within the communities to which we have moved. From the point of view of the French, we are net contributors, not liabilities, while for Britain our absence frees up homes while reducing pressure on social services and the NHS.

Imagine now what will happen if the Government – pressed by Brussels to clear its desk and leave the building ­– opts for a “red, white and blue” Brexit that leaves millions stranded on either side of the Channel. In Britain, millions of tiny flats and shared bedrooms will flood the market, vacated by the Poles and others forced to return home. The howls of anguish from landlords will echo across the oceans, from Dubai to Moscow. But those same flats and hovels will not be filled by returning Brits, who will have to compete with the next wave of immigrants from the Third World – younger, stronger, more willing to put up with everyday discomforts. Instead, former expats, stuffed full of righteous indignation, will demand “proper” homes and compensation from the government that forced them to abandon their dream. Unable to work or pay taxes, this vanquished army of Victor Meldrews will whinge and bitch all the way to the grave.

I don’t say that British policy on Brexit should be driven by consideration of those most immediately affected. Nor do I pretend that a formula will not be worked out that leaves both expat communities effectively in place. Such an outcome would clearly be in everybody’s interests. I do, however, remind those Leavers who argue that we should simply walk out and close the door behind us that, as my Uncle Tommy used to say, God never closes one door but he shuts another.

The case I am putting does, though, raise one obvious question: if a majority of existing EU migrants remains in the UK after Brexit, including those who arrive between now and 2019 – some 3.5 million in all – what are Brits who voted Out supposed to think? And given that the number of non-EU immigrants landing each month already exceeds the total from Europe, where is the mysterious “control” of which the Vote Leave lobby spoke so smugly during the referendum campaign? The truth is that it exists but is almost never exercised. Indeed, more and more, the talk in government and business circles is of a necessary increase in Commonwealth arrivals to make up for the anticipated European shortfall.  Why does nobody in politics talk about this and do they really imagine that Ukip voters will fail to notice?