Steve Connor: Worrying sign that Thatcher's 'brain drain' has returned

The term "brain drain" was coined more than half a century ago to describe the flight of British researchers to the United States in the 1950s and 1960s, when the UK's moribund post-war economy contrasted sharply with the vibrant white heat of American science and technology.

Science is one of the few truly international activities where the market principle operates in terms of human talent. The best people are free to go where they want, provided the opportunities and the money are there – a bit like world-class footballers without the bling.

When economic times get tough, or when government regulations make life difficult, scientists are free to jump ship if they have a good enough track record to compete in the international arena.

Countries have regularly tried to encourage the influx of the best scientific talent. Ten years ago, for instance, the Royal Society and the Wolfson Foundation, a research charity, launched a five-year initiative costing £20m to try to encourage ex-pat scientists back to the UK at a time when the science budget was growing under the former Labour Government.

Meanwhile, the US Congress raised the annual cap on the number of temporary work visas from the most skilled professionals.

Dr Adrian Owen's team is taking advantage of a deliberate recruitment drive by the Canadian government to import scientific stars from overseas, including from across the border in the US, a nation which does more scientific research than any other.

But at the same time as some leading British stem cell researchers have gone overseas others have come to the UK. Perhaps the most notable "reverse brain drain" in this area is Professor Roger Pederson, who came to Cambridge from the University of California, where his research was frustrated by the Bush administration's policies on embryonic stem cells.

The point is that there has always been a circulation of scientific brain power, with many going off for a few years to work with colleagues abroad, only to return home at a later date.

But there is no doubt that when economic times are hard, more scientists tend to leave a country than come to it if government policy allows.

During the savage cuts to the government's science budget under Margaret Thatcher, many ex-pat scientists cited the dire funding climate as one of their main reasons for leaving.

The same is likely to be true in the coming years, given that the UK's science budget is in line for significant cuts while competitor nations, such as the US, France, Germany, Australia and China, have all promised to increase their investment in science.