In July 2012 rules were introduced for people who wanted to sponsor a non-European Union spouse. It didn’t affect our rights to marry foreign nationals; it only applied if we wanted to live with them in the UK. There was a new minimum income requirement of £18,600, calculated by the migration advisory committee as the least you would need to not require income-related benefits (housing costs excluded). They toyed with a higher figure – £25,700 “to offset the potential costs of a two-adult family generated by public spending on services such as healthcare, education and defence”, but that was rejected.

There was very little fanfare about it, and it bobs up only as a footnote to deportation cases: currently, Michael Engel of Cornwall and his wife Natalie are fighting his deportation because her interior design business doesn’t earn enough. It is noted by observers that north Cornwall is in the lowest 10% for average earnings in Britain, and Natalie, with specialist skills and her own business, would be considered by her neighbours to be doing pretty well. The Migration Observatory estimates that 43% of Britons don’t make enough to bring a spouse into the country.

It’s not really about migration, this story: it’s about citizenship. The right to a family life, which includes the right to live in the same country as your spouse, is enshrined in the Human Rights Act but has been part of British law since the British Nationality Act of 1948. It’s a pretty salty document, tacitly considering women the property of their husbands and referring to foreigners as aliens throughout – but one thing it does not do, does not even consider, is splitting citizens’ rights between rich and poor.

But we now operate a two-tier system, where those with money have rights as citizens which those without do not. It’s possible that the threshold is set a little too high, taking in highly skilled people who are only temporarily earning low wages, or unemployed for a short time. That’s vexing but irrelevant; the story here is under what lights this could ever be acceptable, for British citizens to have their rights circumscribed on the basis of their wealth.

From this first principle spin many other assumptions and discriminations. There is sex discrimination going on, plainly – 43% of British people don’t earn enough to bring in their spouse, but that rises to 57% of women, against 28% of men. Once you start measuring a citizen’s worth and standing by their financial muscle, women will be disadvantaged, with their pesky career breaks and maternity leave entitlements. Young people also fall on the wrong side of the rules, being less likely to meet the threshold. And there is a totally unjust anomaly – EU nationals living in the UK are allowed to bring in non-EU spouses, since they are governed by European freedom of movement rules.

For practical purposes, your citizenship is now rubber-stamped on the basis that you claim no benefits; using the social safety net de facto puts you outside respectability, turning you into a burden rather than an asset. This is the foundation of many government pronouncements, but nowhere else has it been inscribed into legislation and tested in a court of law.

Michael Wilson, the judge in the Engels case, remarked that UK taxpayers “should not be expected to have to financially support the appellant in the event of him not obtaining work”. That’s somewhat pessimistic – he might not obtain work, but on the other hand he might obtain a lot of work and himself become one of these UK taxpayers.

But it also accepts, apparently without question, this utterly false dichotomy between the taxpayer and the person receiving benefits. We are all taxpayers – in fact, the campaigner and number-cruncher Simon Duffy has shown that the poorest 10% pay more in tax (income and council tax as well as VAT) as a proportion of their income than any other decile.

In this absolutely nutty system, in which tax can only be explained as a punishment for failing to get rich enough to avoid it, insult is heaped upon injury as judges then characterise the “UK taxpayer” as a special class of person, all themselves in full-time, well-paid employment. And if we are all taxpayers, we are all also benefit claimants – maybe not today, but certainly one day. At what point does respectability kick in for the claimant of state support? At what age are you considered worthy? What kind of disability counts? What kind of need will be classed just dumb bad luck, and not a personal failure? What does Judge Wilson make of statutory maternity leave and child benefit? These are serious questions: if those in receipt of income-related benefits aren’t proper citizens today, those in receipt of housing benefit might not be full citizens tomorrow.

Through the prism of the person, what emerges most clearly is how expensive this new parsimony is: the Engel family has 14 days to fight the judgment– at the end of which, if they lose, they go to South Africa, Michael’s native country. What a waste of a family, which should have been prized. But through the prism of legal principles expressed in the case itself, we can see that everything is at stake: citizenship, social security and ultimately society. Even if the likelihood of your falling in love with a non-EU national is close to zero, this is an assault on your Britishness.