The UK population is set to grow by 25% before 2060
The EU expects to see a big increase in pensioners in the coming decades, with only two people of working age for every person aged 65 or more by 2060.
Deaths will outnumber births in the European Union from 2015 onwards, the EU's statistical office Eurostat predicts in a new report.
By 2060, the UK is likely to have the largest population in the EU - 77 million, ahead of France and Germany.
Despite migration, the EU's population is set to fall from 2035 onwards.
An increase is expected in the next 27 years - from 495 million in January 2008 to 521 million in 2035 - but thereafter Eurostat predicts a gradual decline to 506 million in 2060.
The ratio of pensioners to working-age people is projected to increase, from 25% today in 2008 to 53% in 2060. That translates into only two people of working age for every person aged 65 or more in 2060, compared with four to one today.
The ratio is projected to be more than 60% in the newer EU member states, including Bulgaria, the Czech Republic, Latvia, Lithuania, Poland and Romania. It is likely to be less than 45% in Denmark, the Republic of Ireland, Cyprus, Luxembourg and the United Kingdom.
Eurostat expects big differences in population growth across the EU.
The biggest population growth is expected in Cyprus (+66%), Ireland (+53%), Luxembourg (+52%), the UK (+25%) and Sweden (+18%).
The sharpest declines are expected in Bulgaria (-28%), Latvia (-26%), Lithuania (-24%), Romania (-21%) and Poland (-18%).