LONDON — In the immediate aftermath of last year’s Brexit vote, there was much confusion about what pushed more than 17 million people to put a tick next to “Leave.”

The answer, we now know, boils down to one word: immigration. And yet, since the vote, the political debate has consistently failed to take this into account. If the U.K. continues to focus on trade and the future relationship at the expense of immigration reform, Brexit will only be the beginning of our political trouble.

Concern about free movement, immigration and its impact on the country was clearly the main driver behind Brexit: Studies have shown that people who felt anxious about immigration were not only more likely to play down the risk of Brexit; they were more likely to turn out and vote — and to choose to Leave.

A word cloud reflecting the responses of thousands of self-identified Leavers who, in an open-ended question, were asked in July 2016 why they had voted to pull Britain out of the EU overwhelming answered “immigration.”

Clearly, these worries over identity were wrapped up with broader concerns: a strong sense that the power-brokers and media were not listening to the people; that Britain’s economy, politics and culture lean decisively toward London; and that the country’s political and media class have been too willing to attribute feelings of social and cultural loss to bigotry and ignorance.

Had leaders taken these concerns seriously, the social contract on immigration could have been renewed instead of broken.

Instead, worries were inflamed first by New Labour deciding not to impose transitional controls on EU nationals from 2004, and then by the Conservative Party’s undeliverable promise to reduce net migration from the “hundreds of thousands to the tens of thousands.”

Political leaders consistently underestimated the potency of identity politics and thus Tony Blair and David Cameron were left as the unintended architects of Brexit. Immigration unified traditional and more affluent social conservatives on the right with blue-collar, left-behind workers on the left, and in 2016 this alliance — with a push from UKIP — found its full expression in the vote for Brexit.

A collective failure to ask these questions ... could easily come back to haunt us.

Why does this matter now? The government’s management of Brexit — and its failure to tackle the issues that sparked it — tell us it hasn’t learned from its mistakes and is running the risk of replicating the entire cycle.

As journalist John Harris recently noted, “The only economic rebalancing that looks set to arise from Brexit will be London becoming a bit less rich thanks to the downsizing of the City.” Unsurprisingly, when Ipsos-MORI recently surveyed the population they found that 85 percent of Labour Leavers and around half of Conservative Leavers still feel as though the current system is rigged toward the rich and powerful.

Prime Minister Theresa May insisted in her January 2017 speech at Lancaster House that she would put an end to free movement, and thus take Britain out of the single market. But no one has talked seriously about how to rebuild public confidence on an issue that almost single-handedly sparked the most dramatic change to the political status quo in decades, if not longer.

The debate has focused on trade, economics and — because Britain relies so heavily on financial services — the fate of the City of London. Collectively, we have found sufficient time to debate every possible aspect of our future trading relationship with the EU — from the Norway model to the Canadian model, from the Swiss or Turkish model to a whole range of bespoke models.

We have debated every possible aspect of the economic repercussions; from passporting rights in the City to whether bankers really are leaving us for Frankfurt; from the estimated economic cost of a soft Brexit to the financial impact of Britain crashing out and falling back onto WTO rules.

We have not had a comparable discussion about what a future immigration policy might look like.

Along the way, voters have been subjected to an almost daily avalanche of economic forecasts of the kind that appeared to make no real difference to public opinion, even when it actually mattered ahead of the vote itself.

And yet we have not had a comparable discussion about what a future immigration policy might look like and how this could be built around a public consensus.

We haven’t talked about why so many voters felt the country was moving in the wrong direction. Among those who felt that Britain “got a lot worse” in the past 10 years, 73 percent voted for Brexit. Only 40 percent of those who felt things were “a lot better” did the same.

We put this down to austerity and moved on, conveniently ignoring the fact that the British economy was enjoying its 48th consecutive quarter of growth when UKIP first broke through in 2004, years before the financial crisis hit. With the exception of irregular and largely politically motivated ramblings about creating a northern powerhouse, there is no clear plan for how Britain will rebalance its economy to address the concerns of the nearly 54 percent of voters in England who opted for Brexit.

Our leading parties appear incapable of having this debate. The Conservative Party is beholden to City donors, and Labour is terrified of saying anything about immigration and identity. A collective failure to ask these questions and trigger a more holistic debate over Brexit could easily come back to haunt us.

Imagine, for a moment, a long transition deal that retains the nuts and bolts of Britain’s current EU membership, followed by a slightly watered down settlement that sees the U.K. adopting a liberal immigration regime in return for access to specific areas of the single market. A majority of the British electorate would see it as one that prioritized economics over identity, or London over the nation.

We shouldn’t expect voters to shrug their shoulders if they feel let down by the government yet again. It’s far more likely they will mobilize and move into an even more radical political home that makes Nigel Farage and UKIP look like a fairly quirky brand of old school British conservatism.

Matthew Goodwin is professor of politics at the University of Kent and senior fellow at Chatham House and is the co-author of “Brexit: Why Britain Voted to Leave the European Union” (Cambridge University Press, 2017).