An increasing middle-class "brain drain" of British professionals moving abroad to live and work is raising concerns about future skills shortages in the UK, Home Office research has found.

The study of emigration from Britain reveals that an estimated 4.7 million UK-born people now live abroad, with Australia consistently the most popular destination over the past 20 years.

The research also discloses that, contrary to popular wisdom, fewer people emigrate from Britain at times of rising unemployment as they find it harder to sell-up and fund their move abroad. This is in sharp contrast to the era of the "£10 Pom" 50 years ago when 80,000 impoverished British migrants a year used to sign up for an assisted passage to Australia.

The study found that those moving abroad are overwhelmingly (93%) of working age and that the popular image of Brits retiring to the Spanish Costas is in decline. Only 4,000 people of retirement age moved abroad in 2010, down from a peak of 22,000 in 2006. The fall reflects the end of the house price bubble in Britain during which homeowners could sell up and live more cheaply abroad, while enjoying the better climate and quality of life. The largest numbers of British pensioners living abroad are not in Spain at all but are to be found in Australia, Canada and the US, reflecting the large British communities who settled in those countries years ago.

The Office of National Statistics says emigration from Britain rose sharply over the past decade from 363,000 a year to a peak of 427,000 in 2008. Since then it has fallen back to 350,000 a year. Long-term migrants are defined as those who move abroad for at least 12 months.

British emigrants account for 149,000 or 43% of the 350,000 who left Britain to live abroad during 2011. The remaining 57% were made up of almost equal numbers of European Union and non-EU citizens returning home after living and working in Britain.

It also found that citizens of other EU countries, who face shorter travel distances and lower costs, are far more likely to return home after living in Britain than those from the rest of the world. Migrants from the Indian sub-continent and the Caribbean Commonwealth countries are also more likely to settle in Britain than those who come to live in Britain from Australia, New Zealand or America.

The Home Office study says a large and increasing proportion of British citizens moving abroad are those from the professional or managerial occupations and this has implications for the future availability of skills in Britain.

This group made up just over a third or 37% of British emigrants in 1991 but reached nearly half or 48% in 2010 after a steady year-on-year rise until the global recession of 2008. Most moved abroad to a definite job rather than simply speculative looking for work.

The most recent estimate by the World Bank shows that in 2011 there were 4.7 million British citizens living abroad, representing 7% of the total UK population and the eighth highest of any country in terms of absolute numbers. In percentage terms, countries such as Portugal (21%) and Ireland (16%) have much higher proportions of their population living abroad.

The largest British communities around the world are in Australia (1.2 million), the US (701,000), Canada (675,000) and Spain (411,000).

The Home Office study found that most emigrants intend to live abroad for more than four years and most go to work in a definite job. It said that unemployment and changes in the value of the pound appear to be key factors. But it added, that emigration may now be something that people have to save up for and aspire to and is no longer a desperate throw the dice by the unemployed.

The research found that British emigration to Australia declined after 2006 as British unemployment rates increased. "Put another way, in a time of unemployment individuals' first priority may be to secure some employment at home, and only then when receiving an income will they be able to plan and resource a move abroad," it said.