The coalition government's immigration cap will restrict some universities to hiring fewer than 10 overseas academics this year and may damage the UK's research capacity, critics have said.
Since the government announced its interim cap on immigration from non-European Union countries, the UK Border Agency has told universities that it will impose strict quotas for visas granted under Tier 2 of the points-based immigration system, which covers "skilled" workers.
The quotas cover recruitment between 19 July this year and 31 March 2011, when a permanent cap is likely to be imposed.
For some universities, the quotas were calculated on a 15 per cent reduction from the number of Tier 2 recruits in the corresponding period the previous year.
However, Newcastle University reported that it had been handed a 50 per cent cut.
Veryan Johnston, Newcastle's executive director of human resources, said the university was given a quota of 28 staff, based on a figure of 56 the previous year.
"We are having to monitor this very carefully and day by day to make sure our heads of faculty and pro vice-chancellors understand the potential impact on their areas," she said.
The quotas cover not only visas for new recruits but also renewals for existing staff.
Ms Johnston said that this meant institutions "could lose a key researcher at a critical time".
Chris Marlin, pro vice-chancellor (international) at the University of Sussex, said its quota was in the "high single figures" and reflected a 15 per cent reduction.
The Sussex Centre for Migration Research is among the areas affected, Professor Marlin said.
"All its staff are international...In an international world, it is difficult to study these things without a flow of staff."
He added: "We have had more than 20 years of research assessment with the aim of building up the performance of the UK and making it internationally competitive, which then attracts the best people from overseas. Now we have immigration rules putting universities in a situation that may choke this off."
Professor Marlin said that if the low limits continued under the permanent cap, it would "change the way UK universities operate".
Universities are trying to bridge the gap by encouraging staff to apply under Tier 1, which covers "highly skilled" workers, but the number of visas granted is subject to a national monthly cap.
Elaine McIlroy, senior associate at law firm Dundas Wilson, said universities could apply for extra certificates of sponsorship under "exceptional circumstances" cri-teria, but added that a "pretty tough test" was applied.
Matthew Knight, chair of the Universities Human Resources organisation, warned that a number of universities are close to reaching the limit of their allocations.
"The impact is likely to grow significantly over the remainder of the year," he said, "depending on the attitude that the UKBA takes to the (exceptional) cases made to it."