Among the vacancies for shop assistants and forklift-truck drivers advertised to job-seekers in Hinxton, a village near Cambridge, UK, there are some more specialized positions. A molecular geneticist, for example, is needed to develop scalable technologies for genetic modification of the Plasmodium falciparum parasite. A bone biologist is also wanted, with in-depth knowledge of mouse genetics and endocrine systems.

The adverts are for postdoctoral positions at the nearby Wellcome Trust Sanger Institute, a world-class research centre. Traditionally, the institute has not struggled to fill such posts: if no suitable local candidate came forward, it could always recruit from overseas. Science is a global game after all, and talent has no respect for national borders.

Britain must face the truth: it needs the best scientists more than they need it.

The Sanger Institute is among the UK academic and research institutions now threatened by a clumsy cap on immigration, introduced by the Conservative–Liberal Democrat coalition government. Under interim measures in place until the end of March, the number of workers who can enter Britain from outside the European Economic Area has been strictly limited. Positions at UK universities promised to overseas scientists have already been withdrawn. The Times newspaper, which has turned a much-needed spotlight on the situation, reports that the cap has already seen more than 230 scientists and academics barred from obtaining the necessary entry visas. Some will be eligible to enter Britain next year. Many will not bother.

The great and the good of British science, many of whom come from overseas or have imported team members, have queued up to warn of the folly of such a policy. In the United States, tighter restrictions on entry for scientists — introduced in response to the terrorist attacks in 2001 — have increased the costs and delays of overseas recruitment, hit international collaborations and been widely viewed as damaging to US science. At a time when nations such as China and Germany are increasing investment in their research bases, Britain is turning away some of the people it needs the most.

There is no evidence that UK Prime Minister David Cameron and his cabinet want to pull up the drawbridge against researchers and erect 'British science closed' signs at the airports. But curbs on general immigration were promised by all three major parties prior to this year's election, and the numbers of money-spinning overseas students and those who seek political asylum are harder to restrict than the numbers of skilled workers. The unintended damage to science will be on the agenda later this month, when the cabinet discusses what to do with the cap from April. An exemption for researchers of a certain calibre (similar to the existing route into Britain for overseas star footballers) is one option, but would exclude promising young scientists who have not yet been able to prove their value. Short of reversing the changes this year that saw, for example, reduced importance given to a PhD in the evaluation of visa applications, the most logical step for the government is to restore the freedom for academic institutions to recruit whoever they wish for more junior positions. If necessary, a trial period could be undertaken, and be scrutinized for abuse. Britain must face an uncomfortable truth: it needs the best scientists more than they need it.