Diplomas could replace A-levels as the "qualification of choice" in England, says Schools Secretary Ed Balls.
Mr Balls announced three new Diplomas in academic subject areas - science, languages and humanities - adding to the 14 planned vocational subjects.
Mr Balls also pushed back a planned review of A-levels from 2008 to 2013 to give the Diplomas time to bed down.
He stopped short of predicting A-levels would disappear but would not guarantee their future after the review.
Diplomas, a new type of qualification intended to bridge the divide between academic and vocational learning, are to be introduced from next year, in a limited range of subjects.
'Second-class'
But critics have complained their focus on vocational subject areas, such as information technology and hair and beauty, and the fact that they are to run alongside A-levels mean they could be seen as second-class qualifications.
Mr Balls sought to strengthen the Diplomas while re-assuring parents and teachers that the "gold standard" A-level would not be scrapped in the immediate future.
He told an audience of educationalists and industry leaders at the CBI conference in London that it had been argued that Diplomas could only be a success if A-levels and GCSEs were abolished.
"This is not the government's view and not a matter for us to pre-judge.
"If Diplomas are successfully introduced and are delivering the mix that employers and universities value, they could be come the qualification of choice for young people.
"But, because GCSEs and A-levels are long established and valued qualifications, that should not be decided by any pre-emptive government decision but by the demands of young people, schools and colleges."
Evolution, not revolution
Mr Balls was accompanied by a string of university, college and industry representatives and Sir Mike Tomlinson, who had been the architect in 2004 of a previous proposal for a single qualification, combining GCSEs, A-levels and vocational exams.
The future of A-levels remains uncertain
Sir Mike backed the government's move saying he had always envisioned the replacement of A-levels as an "evolution not a revolution" likely to take about 10 years.
The National Union of Teachers saw the announcement as a clear reversal by the government, showing that the "decision to ditch Tomlinson's 14-19 reform proposals was fundamentally wrong".
Sir Mike is now to join a panel of experts, including representatives from industry and higher education, who will advise on the design of the new qualifications.
The success of Diplomas will depend on how they are recognised by employers and universities - and there were warnings from the previous education secretary that the Diplomas could go "horribly wrong".
If universities continue to use A-level results for their admissions, then the new qualifications will be much less attractive to schools and pupils.
The universities organisation, Universities UK, stressed that the new qualifications will need to "genuinely provide an appropriate progression route on to higher education".
'Subverting GCSEs'
A statement from the Russell Group, representing leading universities, also cautioned that "we are concerned to ensure that the Diploma sufficiently equips candidates with the skills and knowledge they need to flourish on our courses".
The headteachers' union, the ASCL warned that schools were already "punch drunk" with new initiatives and that there would need to be funding and support for schools to take on 17 new Diploma subjects.
But the ATL teachers' union claimed that the government had been too timid in setting out the case for reforming A-levels, saying "they have bottled it again".
The Shadow School Secretary Michael Gove accused the government of subverting GCSEs and A-levels.
"Diplomas were supposed to be about improving vocational education not undermining academic excellence."
Liberal Democrat schools spokesman David Laws said the announcement reflected the government's fears over diplomas.
"There is widespread scepticism in schools about whether they will be popular amongst students," said Mr Laws.
The Diplomas announced on Tuesday will be piloted from 2011.
There have already been 14 Diploma qualifications announced, with the first five - construction and the built environment, creative and media, engineering, information technology and society, health and development - beginning in autumn 2008.
All of the Diploma qualifications will include a basic skills element, in English, maths and information technology.
(www.eduwo.com, Jainlyn&Charlotte)