Picture the scene: a bar or restaurant in Paris, Madrid, Warsaw or Prague. At one of the tables is a couple – one person is British, one is not. They are newly married, and full of plans, but there is one snag. Up until now, they would have been able to settle together in the UK with minimum official fuss. But thanks to the government’s plans for Brexit, all that is about to change.

For the following part of the story, turn to page 66 of the Home Office’s immigration white paper, and its supremely unromantic description of what might happen next. “As a couple, they decide that they want to continue their family life in the UK,” it reads. “The EU citizen considers various work and study options to enter and remain in the UK in their own right, but chooses to enter as a dependent spouse/partner. The EU citizen makes an application with their British citizen partner acting as sponsor, subject to meeting the necessary criteria, including financial independence.”

The definition of what “financial independence” means is in brackets, but this is the most important bit. After either the end of the Brexit transition period or in the event of the UK crashing out of Europe in March, if someone from an EU country wants to apply for a visa as a UK national’s partner or spouse, everything will depend on whether their other half – or “sponsor” – is “earning at least £18,600 per year” – even if the EU national has a job waiting for them in Britain. The same demand already applies to couples where one partner comes from outside the EU, and it has shaped an array of human stories by virtue of one inescapable fact: 40% of the UK’s working population earns less than that £18,600 a year, meaning thousands of relationships are in a heartbreaking limbo.

Because of the gender pay gap, the rules disproportionately affect women. Mandy, for example, lives in Somerset; her partner, George, is 4,500 miles away in Mombasa, Kenya. They are the parents of a toddler called Eric, who has met his father only once, because his mother earns only £12,000 a year and is thereby deemed by the Home Office to be insufficiently “independent” to secure George the relevant visa.

The other day Mandy sent me an email. “I really do not see a light at the end of this barbaric tunnel that is stopping us from being a family,” she said. “So our son will not have his father with him for his third Christmas, and I’m struggling to celebrate anything at the moment.”

Laura lives in Rugby, while her partner, Biniyam, is in Ethiopia; their son, Elijah, has not seen his dad since October 2017. She is now trying to secure Biniyam a visa by citing “exceptional circumstances”, and spending a great deal of money on legal fees. When I met her, back in April, she explained the grim tension between working as many hours as possible to meet the £18,600 threshold, as well as her legal costs, and trying to ensure she spent as much time with her son as possible: the system, she explained, has already denied him contact with his father, so cutting down his time with his mum seems unthinkable.

As stories of delays and lost paperwork prove, the system is already dysfunctional, unreliable and full of unforeseen trapdoors

Around 15,000 children are reckoned to be living without a parent because of a system that should be binned but is now to be extended to people from EU countries – something lost in this week’s media noise about whether the government intends to stick to its net migration target. This move highlights the fact that ending so-called freedom of movement will have consequences way beyond its much‑discussed effects on the economy. Immigration policy, after all, goes straight to the heart of millions of everyday lives, and simple matters of love and family that the cold imperatives of Brexit will inevitably fail to accommodate.

As with so many modern morality tales, this story goes back to Theresa May’s time at the Home Office. Until 2012, any British national who wanted to live in the UK with a husband or wife from outside the EU had only to prove that their other half would have no recourse to public funds. But in the midst of the government’s drive to somehow cut net immigration to the tens of thousands, May introduced what officialspeak calls a minimum income requirement. Living with a non-EU spouse in the UK now hinged on earning at least £18,600 a year (as the theoretical income level at which people do not need any benefits) rising to £22,400 if they wanted to bring a child with them, and an extra £2,400 for every child thereafter.

Savings of £62,500 or more allow the requirement to be waived. The presence of Meghan Markle in whichever country pile she will be celebrating Christmas highlights the fact that if you’re rich and connected, you have nothing to fear. The people whose lives have been ruined, by contrast, are now known as Skype families. My experience of reporting this story suggests that in any British town of a reasonable size there will be at least one of them, struggling to maintain an approximation of intimacy via the internet, and trying to keep a loving relationship going when the government machine seems set on destroying it.

Their numbers will now surely multiply. Even if an EU national who is married to, or romantically involved with, a British citizen does what the white paper suggests and decides to try to settle here “in their own right”, the text makes it clear that their income will dictate their immigration status (before it sets a final figure the government will apparently “consider wider evidence of the impact on the economy, and take into account current pay levels”). And if they attempt to come here as a spouse or partner, the £18,600 figure will definitely apply to their other half – so either way, settling in Britain with the person you love will become an option available only to the relatively comfortably off, and accessible only by manoeuvring through a mess of bureaucracy.

Even then, caveats abound. The relevant visas are subject to renewal every two and half years, and it can take up to 10 to be granted indefinite leave to remain. And as stories of delays and lost paperwork prove, the system is already dysfunctional, unreliable and full of unforeseen trapdoors, so increasing its caseload will deepen those problems. Self-evidently, the world is interconnected and getting ever smaller. People travel and work abroad, and their networks of friends and closest relationships reflect this. To restrict who can live with whom on the basis of an income threshold is cruel. The fact that the policy’s extension will fall disproportionately on the generations for whom precarious jobs and erratic incomes are a common experience is just one more element of Brexit’s inbuilt war on the young.

To the wider world, it sends out an increasingly familiar signal: that Britain is a crabby little island, led by politicians whose desire to flatter the most malignant strands of public opinion too often makes them look like fools. How strange to see a party that professes to loathe the big state and to champion freedom want affairs of the heart subjected to the targets and thresholds of bureaucrats.

• John Harris is a Guardian columnist