Britain gained 333,000 people through immigration in 2015 - a near-historic high that is fanning the debate about newcomers ahead of a vote next month on whether the country should remain in the European Union.
Those who back leaving the EU say Thursday's Office for National Statistics figures prove that Britain can't control immigration unless it quits the 28-nation bloc.
EU citizens can live and work in the other member states - and Britain's relatively strong labour market has proven to be an irresistible draw for hundreds of thousands of workers from the continent.
"You see the pressure on public services, you see the waiting lists in hospitals, in GP surgeries and of course in schools," said former London Mayor Boris Johnson, the leading member of the "leave" camp.
"People are feeling it and what they resent is the lack of control."
London Mayor Sadiq Khan aggressively argued for the "remain" side as the figures were released, arguing that the capital's strength lies in being open to the world.
"We wouldn't be where we are today in London with an isolationist approach," he said. "We know from our experience that the answer is to get more involved, to form more alliances and actively to shape our future in the world.
"That is the British way. That is certainly the London way."
Prime Minister David Cameron, who backs the "remain" side, has long promised to reduce net migration below 100,000. His failure to do so is giving ammunition to EU "leave" activists.
The statistics office says the UK had 630,000 immigrants in 2015, while 297,000 people left.
The net figure of 333,000 is 20,000 higher than in 2014 - a statistically insignificant change - and the second-highest on record.
