LONDON — Britain will become the most-populous country in Europe by 2060 as immigrants to the nation have more children and Germany’s population shrinks.

The British population will swell to almost 77 million from the current 61 million in the next half-century, according to projections released yesterday by the European Union statistics office in Luxembourg. Germany, currently the biggest E.U. state with 82 million people, will shrink to 71 million and France will become the second-most populous country with 72 million residents, according to the report.

The projections reflect a wave of migration to Britain that has bolstered both the workforce and fertility rates in the nation. Europe’s birth rate will decline over the next 50 years, yesterday’s report showed, and the aging population threatens to strain health and pension systems in coming decades.

“We are concerned with finding out whether our member states will be able to pay for the costs linked to aging,” Amelia Torres, a spokeswoman for the EU Economic and Monetary Affairs Commissioner Joaquin Almunia, told journalists in Brussels yesterday. “This is one of the major challenges that Europe must face, together with climate change and globalization.”