A boom in the number of qualifications has seen exam boards become a billion-pound business, a report by the exam regulator suggests.
Ofqual said its estimate of the size of the exam board market was "crude" but totalled pound;933 million for GCSE, A-level and vocational qualifications.
Since 2001, the number of different accredited qualifications has soared from 2,771 to 9,708. Part of the increase has come from the 2,600 now in the new Qualifications and Credit Framework, however, which may include some duplication of qualifications.
Achievements in qualifications other than GCSEs and A-levels, mainly in vocational subjects, rose dramatically from 2.2 million in 2002 to 6.1 million last year, driven by Government's desire for more learning to be accredited.
Colleges say the fees they pay to exam boards have doubled over the past decade from about pound;100 million in 200001 to an estimated pound;200 million last year.
Julian Gravatt, assistant chief executive at the Association of Colleges (AoC), said the increase was not out of line with the growth in college income and provision, but that exam boards' customers were not seeing the benefits of increased efficiency.
He said: "They've made a big investment in IT but that doesn't seem to be reflected in efficiency savings. It's a puzzle as to why exam costs keep going up. Colleges might have 1 per cent in surplus, but exam boards seem to do rather better than that."
But few colleges are taking the opportunity to cut out the middleman and operate as their own exam boards.
City College Norwich was the first to become an awarding body, but did not have any students on its courses for the 200809 year. This year, 17 people have completed its peer review qualifications for college staff and 12 are taking a diploma in policing and public safety developed with Norfolk Constabulary.
Mr Gravatt said the AoC was encouraging colleges to work together to look at how they could get better value for money from awarding bodies.
Building a better understanding of the accreditation system may lead to more of them entering the market, he added.
But colleges may struggle to reach the economies of scale that would allow them to undercut exam boards.
Take-up of the qualifications awarded by businesses which gained awarding- body status has also been slow: Network Rail, one of the first to be given exam board powers, saw just 45 people achieve qualifications in 200809, fewer than the Worshipful Company of Farriers, which trains people to shoe horses.
McDonald's saw 471 of its 65,000 staff pick up its accredited qualifications in the same year.
Of the awarding bodies, Edexcel showed the greatest growth in vocational qualifications, from 66,000 achievements in 2003 to more than 500,000 last year.
An Ofqual spokeswoman said that it did not break the figures down by specific types of qualification, but that the growth was likely to be attributable to BTECs.
Ziggy Liaquat, managing director of Edexcel, said the BTECs had also seen particularly rapid growth in schools in recent years.
He said: "The incredible growth BTEC has seen in the past few years is evidence of the need for reliable work-related qualifications which engage and inspire learners, and which are recognised by both universities and employers."