The case of Wayne Coughlan (see story right) is still under investigation, but has highlighted afresh the debate over the best means of ensuring rigour and quality in the evaluation of achievement.
Professor Alan Smithers, director of the Centre for Employment and Education Studies at Manchester University and a member of the Beaumont Committee of inquiry into standards of the top 100 national vocational qualifications, is among the most influential voices putting the case for a "driving test style" impartial assessment.
He said: "The important thing in making NVQs a national currency is to give them the kind of credibility that A-levels have, by putting in place assessment which is acknowledged to be authentic and consistent.
"This must inevitably involve some element of external assessment."
His comments follow Prime Minister John Major's pledge last month to "root out" bad vocational courses and impose "more rigorous testing and external marking". In a wide-ranging speech to the Grant Maintained Schools Foundation, he said: "No one should doubt my commitment to reversing this country's historic weakness in vocational education."
The Beaumont Committee, due to report to ministers in December, is examining the option of external verification as part of a study of the "top 100" NVQs. Chairman Gordon Beaumont confirmed consultants were considering issues including whether such assessment should be compulsory, apply at all levels and vary in style.
He was wary of pre-empting committee recommendations, but he said: "There must be a variety of methods for assessment, some of which would be more proper in some circumstances than others."
He pledged a toughened attitude to any training provider found bending the rules.
He said: "Any examples found should lead to the automatic revocation of any licence to operate in the future".
The present system, he admits, has left the way open for sporadic abuse. "I think people have felt they can get away with things. That can't be allowed to continue."
Calls for major reforms are driven by dissatisfaction with a system where institutions are allowed to assess their own courses even though funding is partly tied to results.
A damning report on NVQs published last August by the National Institute for Economic and Social Research was highly critical of teaching and assessment, saying results could not be trusted when payment was dependent on outcomes.
Earlier, a Channel 4 programme, All Our Futures, based on a report by Professor Smithers, highlighted concerns over assessment methods.
But an independent inquiry carried out by inspectors from the Further Education Funding Council last year found no evidence that colleges were cheating in vocational exams to boost pass rates.
Professor Smithers advocated a final external check to test if a student can put each newly-gained skill to use. He said the check need not be in the form of a written exam.
For example plumbing or electrical fitting trainees could be given a series of practical tests to show their abilities at the prescribed level.
Others studying subjects such as retailing might be subjected to the "Egon Ronay approach", with external inspectors posing as customers to carry out surprise checks.
Such a process was needed, Professor Smithers said, while colleges, private providers and TECs remain under pressure to achieve results in order to secure funding.
He said: "Payment by results is acceptable if you can be sure that people are being raised up to a set level, but if the assessment is moveable it is likely to go down to meet what is convenient to the providers."
Mr Beaumont rejected suggestions of widescale fraud surrounding vocational examinations. He added the problem has been greatly exaggerated: "You only have to have one example for everyone to believe it is rife."