LONDON — Fewer work and study visas contributed to a near-halving in net migration into the U.K. — the number of people moving to the U.K. minus the number of those moving abroad — in 2024, official figures showed Thursday.

The Office for National Statistics said the figure stood at an estimated 431,000 in the year, down 49.9% from 860,000 a year earlier. That’s the biggest percentage decline since the height of the coronavirus pandemic in 2020, and the largest numerical drop for any 12-month period.

Britain has relied on people coming into the country legally to contribute to economic growth, certainly in the decades after World War II, when millions arrived to help rebuild the country. And for years, it wasn’t much of a political issue and on the periphery of debate.

But it has become a politically toxic issue over the past 20 years or so, and played a key role in the Brexit vote of 2016, when Britain voted to leave the European Union. Membership of the EU comes with the obligation to offer free movement to all citizens of the 27-country bloc.

But immigration figures have gone up, not down, post-Brexit.

The anti-immigration party Reform U.K. won big in recent local elections and is ahead in many opinion polls. Its argument is that too-high immigration is impacting on public services, housing and societal cohesion as a whole.

The figures released Thursday do not include those arriving in the U.K. by unauthorized means to seek asylum, many in flimsy, small boats across the English Channel. Though that number is far lower — some 37,000 people crossed the English Channel on small boats last year — it’s amplified the heat surrounding the debate.

A more detailed look at Thursday’s figures shows that the biggest contributor to the fall was a sharp decline in immigration, with the number of people coming into the U.K. below 1 million for the first time in around three years. However, the statistics agency also found that emigration swelled back to 2017 levels.

The number of arrivals in the U.K. surged from 2022 onward, driven by many factors, including the more than 200,000 people fleeing Russia’s war in Ukraine and more than 150,000 from Hong Kong on special overseas visas.

The period covered by the latest estimates follows the introduction in early 2024 by the then Conservative government of restrictions on people eligible to travel to the U.K. on work or study visas. Though the Conservatives, now the main opposition party, have sought to claim credit for the decline, one of the main reasons they were swept from power after 14 years was the increase in net migration levels to record highs.

In August, weeks after the Labour government took office, the country was convulsed by anti-immigration riots in which mosques and hotels housing asylum seekers were attacked.

Labour Prime Minister Keir Starmer is seeking to get net migration levels down further and earlier this month set out a series of measures aimed at reducing further the number of people moving long term to the U.K.

Starmer said the country risks becoming an “island of strangers” without better integration, and said he wanted net migration to have fallen “significantly” by the next general election, but without giving a specific target.

His plan includes reforming work and study visas and requiring a higher level of English across all immigration routes. Experts think that could reduce the number by a further 100,000 a year.