It is claimed people sign a register but do not attend lessons

The move, by the Association of Colleges, follows a new claim that a college was used by people to obtain UK entry visas and to work, not to study.

The government is in the process of tightening up the system by compiling a register of bona fide institutions.

The Association of Colleges said making this voluntary did not go far enough.

The director of international relations at the association, Jo Clough, said the scheme was better than nothing.

Without it, the reputation of UK universities and colleges was open to damage or abuse by bogus and non-quality accredited institutions, she said.

Any institution not up to core minimum standards should not be allowed to trade in the field of education Jo Clough, AoC

The experience of many further education colleges was that there had been confusion and an inconsistent approach to what determined a "genuine institution" in many countries, by both potential students and visa entry clearance officers.

But she said that what was being done did not go far enough.

"The government prefers a voluntary scheme, as it claims mandatory accreditation could 'put many providers out of business if the standards were too high for them to meet'," she said.

"The AoC believes this is not an acceptable or ethical argument.

"All institutions in receipt of public funds, as well as the many private institutions carrying other forms of recognised accreditation, have to undergo rigorous (and often expensive) inspection regimes.

"If we are to protect professional standards in the education and training industry and preserve the reputation of the UK as a quality choice for study by overseas students, all serious learning providers who wish to appear on the list must make that same commitment to quality.