Immigration Minister Phil Woolas has defended the government's new points based visa system for foreign students against claims it is easy to abuse.
Border Agency staff claim they have little power to challenge suspected cases of abuse under the new rules.
Mr Woolas told the BBC the system was a "huge improvement on the past."
The UK refused alleged bomber Umar Farouk Abdulmutallab a student visa earlier this year. He has been charged with attempting to bomb a US airliner.
The government began rolling out its points-based system for prospective migrants from outside the EU in February 2008.
To qualify for a visa, non-EU students have to show a letter of acceptance from sponsors (either an accredited college or university) earning 30 points.
The remaining 10 points needed are earned by their proving they have the means to pay course fees and expenses.
Border Agency staff have told the BBC this largely paper-based process is open to abuse.
However Mr Woolas rejected the claims.
"There will always be examples of people who try to play the system," he told The Report on BBC Radio 4.
But he added: "I'm not denying that there aren't problems but what I would say is that this system is a huge improvement on the past."
Around a dozen Border Agency staff have contacted the BBC in the past two months to complain about the new rules for student visas.
The alleged air bomber Umar Farouk Abdulmutallab applied for a visa to return to the UK following the completion of his three year degree in 2008.
But the Nigerian student was refused entry to the UK earlier this year after applying to study on a bogus course.
He has been charged with attempting to bomb a plane as it came in to land at the American city of Detroit on 25 December.
Nevertheless the whistle-blowers who contacted the BBC claim they are virtually powerless to challenge suspected cases of immigration abuse once a non-EU national arrives at a UK port because all checks are carried out overseas.
One entry clearance officer (who did not wish to be named) told the BBC that in his last posting in India he never met an applicant face to face in six months.
"I never spoke to anybody and the important thing was to make a decision.
"Most of the colleagues I was working with, I know they never did because they have similar misgivings to myself."
He claimed a culture of targets meant there was pressure to grant visas and he alleged the new visa rules had led to an increase in applications.
The officer said he had seen lots of students who were refused under the previous rules gain entrance to the UK.
Sir Andrew Green, chairman of the think tank Migration Watch, himself a former diplomat and a critic of the changes, said previously applicants had to satisfy an immigration officer they were genuine.
"Now it just goes through a system because it's paper based, tick the boxes, produce the documents in you go," he added.
But Mr Woolas told the BBC, "The number of people who say that migration controls are too tough, far outweighs the opposite accusation."
The Report is on BBC Radio 4 on Thursday, 31 December 2009, at 2000 GMT. You can also listen via the BBC iPlayer after broadcast or download the podcast.