Perhaps the most dispiriting thing about the migration debate is the extent to which those with the best of intentions are often the least willing to accept any evidence that runs contrary to their abstract principles.

Plenty of well-meaning individuals seem to want to bury their heads in the sand as to the challenges that migration brings with it because they do not, for perfectly understandable reasons, want to give credence to the most contemptible people in Britain: those whose hostility toward migration is motivated by xenophobia and racism.

Thus, in recent years, liberals and leftists have been dealing with problems either too late or not at all, and with deleterious consequences: had liberals paid a little more attention to the views of the so-called 'left-behind' voters prior to lecturing them and, in the US, offering them Hillary Clinton, we might be hearing a little less of the 'Oh, 2016' shtick about now.

Political grumbles are like cancerous tumours – they do not disappear if you ignore them, but grow unfailingly until the danger is a good deal harder to address. By not acknowledging problems earlier, we are today confronted by the onward march of politicians who are willing to deal with them in a far more ugly and illiberal way.

In Britain this ugliness has even bled over into the trade union movement. Such is the anti-migration atmosphere in Britain right now that in the race to become the new general secretary of Britain's biggest trade union, both the incumbent Len McCluskey and his main challenger Gerard Coyne have called unambiguously for restrictions on migration from Eastern Europe.

McCluskey has described free movement as an "experiment at UK workers' expense", while Coyne has claimed that Unite members would "feel betrayed" unless immigration curbs are introduced and has called the issue "non-negotiable".

On one hand this is demagogic electioneering. However both McCluskey and Coyne are undoubtedly responding to the prevailing mood among Unite members. There is a clamour to restrict or halt altogether the movement of poorer eastern Europeans to Britain, especially among working-class Britons.

For years, liberals have tried brushing this attitude under the carpet, or else they have got on their soapboxes and delivered pious lectures. Neither have worked, and today, alas, we are getting the ugly and illiberal purported solutions.

Broadly speaking, of course, immigration is good for Britain. There is a mountain of evidence to suggest that it brings a great deal that is beneficial to the country, including economic benefits (most of those who come to Britain want to work and are young, hard-working and educated) as well as cultural diversity ("What do they know of England, who only England know?" as Rudyard Kipling's lament 'The English Flag' had it).

But what is perhaps most frustrating from the point of view of those who broadly support immigration is the way in which liberals so often try to make out that it is all sunshine and rainbows – that migration on a significant scale does not bring with it any new challenges. You can, for example, acknowledge that a labour market with a preponderance of cheap labour tilts the power balance toward employers and believe simultaneously that there are better ways of tilting it back than draconian immigration controls.

Liberals so often try to make out that it is all sunshine and rainbows – that migration on a significant scale does not bring with it any new challenges

Every working person knows this, but nearly every progressive middle-class liberal will have some spreadsheet stored away which at the opportune time he or she will pull out to 'prove' that it is not so. Last year I spent about six months working at the bottom end of the economy researching a book, and one big agency plainly informed us on the very first day of a job that there were "70 eastern Europeans waiting" for the work that we were doing.

The message delivered to us was unambiguous: 'Don't rock the boat because we can replace you as easily as a burnt-out lightbulb'. I heard similar boasts in several jobs, and was told of comparable experiences by co-workers.

A year ago I would have probably waved aside similar claims with a folder of dry economic data from some obscure ONS report. But since then I have come to realise that this is the default response of the 'bubble' that swathes of politicians and commentators, myself included, inhabit.

This is not the 'liberal metropolitan' enclave that fraudulent anti-elitists such as Nigel Farage drone on incessantly about – there are plenty of poor people in the metropolis too, and many of them are both brown-skinned and liberal.

But there does exist a discernible bien pensant willingness to pretend that immigration has no impact whatsoever on worker-employer relations, and this attitude is a luxury bred of the separateness of middle-class life from the flesh and blood reality of the 'left-behind' – or the working classes, as they were once called.

The fuzzy consumer world of Spanish baristas and cheap Polish builders is, in reality, a long way from the agency worker's world of production lines and social care. This is where mass migration ensures that the message is rammed down your throat, like medicine to a child, and that there is always someone more desperate than you and with fewer quibbles about workers' rights breathing down your neck.

You can get a sense of the prevailing liberal confusion in the way in which some of the major economic squabbles have been turned upside down in recent years. At one time it was free market fanatics who desired 10 workers chasing every job.

Today it seems to be the raison d'être of well-meaning Remainers: a dozen eastern Europeans obsequiously begging for crumbs from the table of big business is supposedly a huge boon, both for the toilers themselves and as for the indigenous workers forced to compete with them for scraps.

Yet it is precisely the unwillingness on the part of liberals to acknowledge the challenges for the working class that migration brings (I will invariably be denounced for writing this article, even though I support free movement) that is rendering the political climate gradually more inhospitable to those who want to find solutions that do not involve sealing off Britain's borders.

As 2016 ought to have demonstrated to everyone on the left, the first consequence of political underreaction is typically a crude and ill-thought-out overreaction.

James Bloodworth is former editor of Left Foot Forward, one of the UK's top political blogs, and the author of The Myth of Meritocracy.