Record numbers of Britons are leaving - many of them doctors, teachers and engineers - in the biggest exodus for almost 50 years.
There are now 3.247 million British-born people living abroad, of whom more than 1.1 million are highly-skilled university graduates, say the researchers.
More than three quarters of these professionals have settled abroad for more than 10 years, according to the study by the Organisation of Economic Co-operation and Development (OECD).
No other nation is losing so many qualified people, it points out. Britain has now lost more than one in 10 of its most skilled citizens, while overall only Mexico has had more people emigrate.
The report is a statistical analysis which does not study the motivation for leaving Britain. However, high house prices and taxes and poor climate are frequently cited.
The term brain drain was coined in the 1950s following the mass emigration of scientists and other experts to America. Tens of thousands of people also left the country to escape the industrial unrest and high taxes of the 1970s.
Damian Green, the shadow immigration minister, said: "Ten years of Labour has re-created the brain drain. High taxes and Government interference are driving people away."