The number of private English language colleges that could be providing illegal immigrants claiming to be students with a route into the UK has fallen by nearly 95%, new research has shown.

English UK, the organisation of accredited state and private language centres, said the number of non-accredited establishments which could be recruiting students in breach of immigration rules had fallen by almost 95% in the past four years.

Chief executive Tony Millns said 45% of previously non-accredited colleges were no longer operating as English language schools, while 27% are recruiting EU students only and so not a concern in immigration terms. He said 22% had achieved some form of accreditation.

In a letter to immigration minister Damian Green, he said: “We believe that this [research] shows that the changes introduced up to the start of last year were having, and continue to have, an extremely beneficial effect: 45% of the previously non-accredited are no longer operating as English language schools; 27% are recruiting EU students only and are therefore also not a concern in immigration terms; and 22% have achieved some form of accreditation that is at least better than nothing.”

English UK said only 6% of the original 560 language schools monitored by it since 2002 were still giving cause for concern compared with four years ago, when checks found the vast majority were still active.

Mr Millns said it had continually raised the issue of “bogus colleges” as an immigration loophole with the Border Agency and the last government “for years before anyone took any notice”.

He said sorting out the non-accredited sector would have far more impact in reducing abuse of the student visa route than several more recent initiatives.

English UK originally created its database of 560 non-accredited English language schools to get an idea of the scale of the problem amid concerns they were a source of “blatant abuse of the student visa system”.

It said the accuracy of the database was confirmed by a consultant working for the British Council in 2004.

That year the government clamped down on bogus language colleges, announcing a register for colleges to “provide evidence of their legitimate business” and the possibility of refusing to grant student visas to applicants who planned to attend a college not on the register.

Today English UK said a recent survey carried out by one of its researchers this spring identified just 33 schools - 6% - as still giving cause for concern.

It said this was because, when approached during a “mystery shopper” exercise, they appeared to agree that they could accept an adult Russian student on a short course, despite not being accredited to take visa students.

Mr Millns added: “This could potentially be error or lack of understanding of the student visa system on the part of the person we spoke to, but we obviously have no power to investigate that further.”

Mr Green said: “We are pleased that the English UK survey confirms that the changes we have made are biting hard on those who don’t play by the rules.

”This Government has introduced radical reforms in order to stamp out abuse and restore order to the uncontrolled student visa system we inherited.”