The UK could have a sudden reversal in population numbers due to the success of its vaccine drive, after the pandemic sparked an "unprecedented" exit of foreign-born workers, a leading economist told <em>The National </em>on Wednesday. Figures from the Office for National Statistics suggest almost a million people born outside Britain may have returned to their home countries last year, the biggest net outflow of foreign-born workers on record. There were 795,000 fewer foreign-born workers in Britain in the final three months of 2020 than a year earlier, and nearly a million fewer foreign-born residents aged over 16, according to the statistics. The figures come from an official survey of Britain’s labour market, not the main immigration data, which has been suspended due to the pandemic. For this and other reasons, the ONS said, the figures should be “used with caution”. The data also show that between February and November last year, the number of full-time UK employees dropped sharply, although pointed to a slight recovery in recent weeks. The method by which responses to the survey are quantified assumes the UK's overall population still grew at its pre-pandemic rate, potentially giving a misleading starting point for the estimates. The survey was not designed to capture migration flows, and the pandemic means phone calls have replaced door-to-door interviews. This makes it harder to tell whether fewer foreign-born respondents reflect a change in the sample or an underlying change. But Jonathan Portes of King’s College London, who was chief economist at the UK’s Department for Work and Pensions, said there was “no doubt” that at hundreds of thousands of foreign-born workers, if not more, returned home. "This is unprecedented in British economic history, as far as we know," he said<em>. </em> “It’s probably the first time that the population overall has shrunk in the last 40 years. It’s probably the biggest fall in population since the Second World War. Historically, this is a big deal.” Prof Portes said many of the foreign workers who left the country last year would have been employed in the hard-hit hospitality and events industries forced to close during rolling lockdowns. He said those workers could be poised to return to the UK as the country emerges from lockdown, based on the success of the vaccination programme. More than 17.9 million people have so far received a first dose of a vaccine, statistics show, with the government aiming to have all adults inoculated by July 31. "There is a positive scenario in that we are worse hit than other countries because we mishandled the pandemic so badly, but maybe we will recover better than other countries because of the way we have handled the vaccination programme," Prof Portes said. "In May, the UK was one of the worst places to be in the world, but this summer the UK [will be] one of the best places to be. "In that case you could see a very sudden reversal – perhaps the statistics are not long-term significant. “There is obviously a pessimistic scenario where we recover, but the recovery is slow and painful and that could have quite significant consequences for the UK in general.” He said the UK’s unemployment rate of 5.1 per cent could have been higher if it wasn’t for foreign-born workers going home, shrinking the labour market. “Immigration and labour market flexibility helps propel job growth and it’s pushing down on it in the same way,” he said.