An investigation is under way into claims that plumbing apprentices were wrongly awarded their qualifications.

Former Unitec head of plumbing Garry Cruickshank made the claims to Tertiary Education Minister Steven Joyce last year.

He alleged the Plumbing, Gasfitting and Drainlaying Industry Training Organisation had knowingly created a substandard course, ignored warnings it would not meet industry standards and passed students who had failed.

ITO chief executive Ian Elliott has dismissed the claims, describing Mr Cruickshank as "an obnoxious litigant who's hounded us for a decade on a personal crusade".

Mr Joyce has referred the matter to the Tertiary Education Commission and the Qualifications Authority to investigate.

In his complaint, Mr Cruickshank said the ITO had switched apprentices from his former course at Unitec to a shorter, cheaper course at the Manukau Institute of Technology, which he ended up teaching.

He said the students were supposed to learn the theory in advance but much of the material supplied was incomplete or wrong.

The practical tasks set for the course did not cover the unit standards required for the qualification. When he raised the issue, he was told to keep teaching the material.

Mr Cruickshank refused to pass 24 students in three intakes as he said the work did not meet the standards. The ITO replied that there was only one missing standard for gasfitting.

Students were reassessed on this but many failed again. Despite Mr Cruickshank's objections, the ITO said they could pass the assessment by sitting a written test at home in their own time.

Mr Cruickshank said he and two other tutors believed some of these students were potentially dangerous as gasfitters.

Some students failed the re-sit test in April but the ITO had registered their qualifications in February, as if they had passed.

Mr Elliott said Mr Cruickshank had worked against the course from the beginning because he opposed its introduction in place of his course at Unitec.

Unitec sacked Mr Cruickshank last year for warning plumbing firms and students not to take the new course. Mr Cruickshank has appealed against his dismissal to the Employment Court and is waiting for a decision.

The head of building and construction at MIT, Paul Jeurissen, said he was disappointed Mr Cruickshank had used his position at MIT to argue his case in public.