Reality is at last dawning. The home secretary, Sajid Javid, is reportedly to propose that EU passport holders will be waved through immigration “for 30 months”, in the event of a no-deal Brexit next March. They will only need to apply for visas later, if they wish to stay permanently.

This is reportedly a concession to business, employers and the chancellor, Philip Hammond. They have been frantically pointing out that farms, hospitals, care homes, construction sites, hotels and restaurants will simply close if their regular input of EU labour, skilled and unskilled, dries up from March. It is already declining at the prospect of Brexit. Stopping it or smothering it with bureaucracy would be the most savage act of self-harm by a British government in living memory.

The truth is that Javid has other problems. It is an open secret that Home Office officials have told him they cannot possibly construct a hard border for all EU visitors at ports of entry by next March. They cannot even contemplate one in Northern Ireland, where the argument is still over lorries, let alone people. Free movement of EU citizens will remain of necessity, until some hard-Brexit thinktank can devise an alternative to the free market in continental labour, so ardently championed by their hero Margaret Thatcher in 1986. They have 30 months to do so, or it will be 30 years.

Reporters returning last week from Salzburg expressed dismay that few heads of government seemed to care about Brexit. It was a minor local trouble on the fringe of Europe. Overwhelmingly they cared about migration. All face an anti-immigrant electoral backlash and many are now installing border controls. While the issue is mostly non-EU migrants, open borders are likely to be the first of the single market’s four freedoms to crumble.

This makes Brexit bitterly paradoxical. Leave voters were never worried over trade or tariffs, and no survey suggests otherwise. Brexit was driven by a concern with immigration. Yet at the very moment when the EU agrees, and starts to tackle it, Britain jumps the gun and leaves in a huff. Now, to pile irony upon irony, Britain’s home secretary moves in the opposite direction. Britain’s EU border must remain open for the simple reason that he cannot close it. Closure is economically harmful and practically impossible.

Perhaps Javid should talk to those of his colleagues now talking of a Brexit “Canada option”, defying Theresa May’s frictionless border pledge. This would impose border checks on all exports – merely admitting roughly half tariff-free. It would also require Britain’s tradable products, including food, to meet EU regulations, over which Britain will have surrendered all control.

If Javid can “wave through” people on grounds of economic expediency, he can surely wave through trade. That is called membership of a single market. With each passing day, we learn that leaving it is massively against Britain’s interest. It is perhaps no surprise that Brexit fanatics tend also to be climate change deniers.

• Simon Jenkins is a Guardian columnist