This man said he paid to extend his student visa - so he could work

The Association of Colleges said the visa loophole exposed by the BBC should have been closed at least a year ago.

It said the rules about who could be included on the official register of colleges needed to be tightened.

Language college group English UK, which runs an accreditation scheme, said it had also warned the government.

The official register was introduced in January last year in response to long-running concerns about "visa mills".

'Wide open'

The chief executive of the Association of Colleges, Dr John Brennan, said: "The register has given an air of legitimacy to private operations without any real safeguards to ensure that they do not abuse their position.

"We warned the Home Office repeatedly last year that creating a register which allowed anyone on it was wide open to abuse. There were no checks on quality or probity."

The register was compiled using lists of training organisations provided by funding organisations.

These resulted in some curious entries, such as prisons, the Archbishop of Canterbury and locations such as a coffee shop in Nottingham.

False papers

Dr Brennan's association wants the Home Office to restrict the register to bona fide colleges which are in receipt of public funding or are properly accredited by English UK.

"That way, both legitimate students coming in to study from overseas and the public are properly protected," he said.

A BBC investigation at a private English-language school in London uncovered a student apparently being sold false enrolment papers even though she made clear she had no intention of attending classes.

Others paid up to �350 for the papers they needed to extend their stay in the UK, to a school that was on the official register.

Immigration minister Liam Byrne said checks were being made to identify and remove bogus schools from the register.

A quarter of the 1,200 initially on the list had been found not to be genuine, he said.