The man who inspired the Government's flagship Diplomas has dealt a major blow to their credibility, warning they need structural change to stand a chance of meeting ministers' ambitions.
Sir Mike Tomlinson has told The TES he fears the controversial academic versions of the Diploma, due to be introduced next year, will suffer from "far less" subject knowledge and content than A-levels, making them unattractive to universities.
His comments are particularly embarrassing for the Government, as it recruited Sir Mike as a "champion" for the new qualifications.
The former chief schools inspector was sitting alongside Ed Balls in 2007 when the Schools Secretary announced them, saying he hoped they could "become the qualification of choice".
This week Sir Mike said this was only likely to be achieved with the "vocational" version of the qualification. "I think it's much less likely for the ones that are designed to be, as is referred to, the academic Diplomas," he said.
In an outspoken interview he also revealed for the first time that he thought ministers' handling of the National Challenge scheme - another Government initiative he advised on - had been "unfortunate".
The "academic" Diplomas in science, humanities and languages were designed as qualifications that could rival A-levels.
But this was now in doubt, Sir Mike said. "I think there is a huge commitment to the A-level and until such time as an alternative is shown to be better than the A-level, people will want to stick with what they know."
The 14-19 expert, whose 2004 report inspired the Diplomas, said the "academic" versions could only become the qualification of choice if "the construction of the Diploma is got right".
Sir Mike said he was "not convinced at this point in time" that it was right. He said the Diplomas would have no more teaching time than the equivalent A-level courses, but because they required knowledge to be applied, which took time, something else would have to give.
"My worry is that the result of that may well be that we have far less knowledge, content, concept and understanding in what we do than is currently in A-level, which I think would greatly worry higher education," he said.
Sir Mike was speaking as an inquiry he chaired into vocational education called for an end to a two-tier system that it said relegated further education lecturers to a "second division" in pay and status, compared with their school counterparts. School and FE college staff are increasingly being required to work closely together to deliver Diplomas.
The Skills Commission inquiry also called for "convergence courses" for college principals and school heads, so that they can transfer between the two sectors.
It found that school teachers leading vocational courses sometimes had no work experience in the relevant area. It recommends regular placements with employers to allow them to keep their knowledge up to date.
Sir Mike's Diploma warnings are only the latest in a long line of blows to the qualifications. In September The TES revealed that none of them would survive in their current form under the Conservatives, who have already said they would scrap the "academic" versions.
A Department for Children, Schools and Families spokesman said: "Diplomas are delivering the mix of theoretical and practical skills that employers and universities value and for this reason they could indeed become the qualification of choice for young people."
He said the department made "no apologies" for "striving to increase standards in secondary schools" through the National Challenge.
Sir Mike Tomlinson chaired a panel of "expert advisers" for the National Challenge when it was launched in 2008. But this week he accused ministers of using the scheme to hold the "Sword of Damocles" over schools.
The former chief schools inspector said he was free to speak out now that he was less involved with the controversial school improvement programme.
"It wasn't helpful to talk about them as failing schools and to hold the Sword of Damocles over them that `if you don't improve we'll close you'," he said. "It has changed over time. I think it's the language used, not the underlying desire to improve the schools. But the language used around them was most unfortunate."