The Tomlinson plan has far-reaching implications

The Qualifications and Curriculum Authority has published its advice to the Education Secretary, Ruth Kelly, as she finalises her response to the plan.

A head teachers' leader called it "a shot across the government's bows".

The QCA said the potential "step-change in participation and attainment" lay in the integrity of the whole diploma.

"Any partial implementation of the proposals would, in our view, compromise that integrity."

'Here to stay'

The Tomlinson working group, set up by the government, proposed a four-level diploma replacing GCSEs, A-levels and all the vocational qualifications for teenagers.

Widespread public support is of paramount importance Sir Anthony Greener

The government is expected to publish a White Paper shortly, setting out what it plans to do.

But the initial response from the Prime Minister, Tony Blair, was that GCSEs and A-levels would stay.

Last week David Bell, the head of the education inspectorate, Ofsted, said he thought they should disappear.

"If we don't say this is a sea-change in education, we will miss a great opportunity," he said.

Learning lines

The advice from the QCA, in a letter approved by its board and sent in the name of its chairman, Sir Anthony Greener, takes the same line.

It recommends that "commitment to the proposals is signalled now".

His letter identifies eight "strategic issues", of which the interdependent nature of the proposals is the first.

Others include the importance of the concept of "lines of learning" so that youngsters are not "locked into" making "irrevocable choices at an inappropriate age".

This is an approach the QCA has been working on for some time in its own reform of vocational qualifications.

Its director of qualifications and skills, Mary Curnock Cook, told the BBC News website a year ago that the notion that 14-year-olds would have any idea what they wanted to do as adults was "preposterous".

Assessment

The QCA also says that - although Tomlinson envisaged diplomas at four levels of attainment - in the longer term people should be certified only once, "at the highest level they reach".

Such a move would also do away with GCSEs as a sort of progress check even if children are staying in full-time education.

But the QCA stresses that "widespread public support is of paramount importance", so assessment of people's achievements must be "at least as rigorous as they are at GCSE".

The QCA envisages "significant initial investment" in setting up a database to track and record youngster's various achievements in a transcript.

It talks of the "massive potential" of electronic assessment methods.

'Shot across the bows'

The Secondary Heads Association said the QCA advice was "a shot across the government's bows".

Its general secretary, John Dunford, said it also wanted to see the Tomlinson report implemented "without cherry-picking its elements to fit a political agenda".

"The prime minister's declared intention to retain A-levels and GCSEs threatens to undermine the integrity of the Tomlinson proposals."

A-levels and GCSEs needed to be "building blocks" in the new system but ultimately must be replaced by a diploma.

Secondary heads wanted a more coherent approach, with academic and vocational qualifications as part of the same structure, Dr Dunford said.

"The Tomlinson recipe provides this coherence and we strongly support QCA's contention that it should not be unpicked."

The Conservative Party has proposed reverting to the system as it was until the 1980s, with only a fixed proportion of A-level students being awarded A grades - and state schools offering O-levels if they wished.

It said on Friday: "Rather than pointing the way towards higher standards, the QCA has vigorously led the path downhill.

"In its present form, the QCA is not part of the solution - instead it is the heart of the problem. It needs radical overhauling?

The QCA letter said it believed the need to differentiate between equally well-qualified A-level candidates could be met "by making greater use of information available from the current system".