UK universities could lose thousands of overseas researchers because of changes to the visa system that will leave scholars without a clear route into the country, Universities UK (UUK) has warned.
As part of the move to a points-based immigration system, the so-called "sponsored researcher" visa was officially abolished for new applicants from last week.
The visas were given to overseas academics who came to participate in research at UK universities but whose salaries continued to be paid by their overseas institutions.
UUK said that more than 2,000 sponsored researchers came into the UK each year and - as they often stayed for two or three years - it was likely that, at any one time, there could be at least 5,000 people in the category.
But under the new system there is no direct equivalent route into the country for such staff. Instead, skilled workers can enter the country under "tier 2", but this option requires the incoming researcher to have a job offer from a sponsor UK university. A "tier 5" option for temporary workers contains no specific category for researchers.
A UUK spokesman said: "The position of sponsored researchers within the new points-based immigration system remains unclear as their previous entry route has now closed. Universities UK is very concerned that this group of highly skilled people will now be unable to come to the UK to contribute to our research work."
He added that universities were "already reporting" the loss of researchers to other countries due to the closure of the sponsored-researcher route.
"We will continue our discussions with the Government to try to find an appropriate way forward to enable this type of researcher to continue to come to the UK - but the longer this situation goes on, the more damage is done to the UK's higher education system," he said.
A UK Border Agency spokeswoman said discussions on the arrangements for sponsored researchers were ongoing between the Government and members of UUK.
She said: "Universities can directly sponsor named researchers under tier 2 of the points-based system." She said that sponsored researchers could also enter through tier 5 - government authorised exchange - as temporary workers.
"This route requires the researcher to be on a research programme authorised by a government department and operated by an overarching sponsor," she added.
Short-term "academic visitor" visas, which are used by those on sabbaticals, remain outside the points-based system.