Heads’ leaders have delivered a damning verdict on the new national curriculum, warning that it cannot be introduced in the time allotted, and that it could “create chaos” and result in lower standards.

Secondary heads have rejected the proposed curriculum’s strict focus on content and want implementation delayed beyond 2014. Primary heads say the government has reneged on its promise to provide them with room to innovate and has failed to get teachers on board.

The condemnation came as it emerged that a senior civil servant has admitted that one of the most controversial aspects of the curriculum was written internally by the Department for Education, without any input from experts.

Criticism of the draft curriculum has been growing since it was first published in February, with history coming in for particular censure. Classroom teachers used the Easter union conferences to belittle “Gradgrind Gove’s pub quiz curriculum”, claiming it would lead to truanting by bored students. Last month, 100 education academics wrote an open letter warning that the changes would damage standards by promoting “rote learning without understanding”.

But the latest criticism is particularly damaging because it comes in a formal response to the official consultation, from the heads who are essential to making the reform work.

Brian Lightman, general secretary of the Association of School and College Leaders (ASCL), said the proposals “cannot be implemented by 2014 within the same time and resources available to schools” and called for the consultation period, which closes on Tuesday, to be extended.

The ASCL said the “vast majority” of secondaries were happy with the existing national curriculum and warned that its replacement could be “detrimental” to standards.

The proposals “could create chaos if implemented in their current form and to the intended timescale”, it warned.

The union also fears that nothing is being done to address a “severe shortage” of teachers equipped to teach certain areas of the new curriculum, such as computing and languages, and has a series of major concerns about individual subjects (see box).

Worryingly for the government, the ASCL also appears to reject the idea at the heart of the reform - that the national curriculum is restricted to content and what to teach. It said that while it was helpful to specify content, “it is also essential that the national curriculum engages with how students apply that knowledge”.

Russell Hobby, general secretary of heads’ union the NAHT, does not oppose the new curriculum’s focus on facts. But he is concerned that too many are included and that the government has failed to listen to teachers and to sell its reform to the profession. “If teachers don’t believe in the curriculum it won’t work,” he said. “Because once that classroom door shuts, it is what inspires teachers that gets done.”

Mr Hobby, who had yet to finalise the NAHT’s response to the consultation, said the government had “specified the ‘what’ so extensively and so tightly that it has constrained or dictated the ‘how’”. He added: “We are still looking for evidence that the government is creating the freedom it promised at primary level.”

Meanwhile, Matt White, assistant director of the DfE’s national curriculum review, has revealed that the controversial design and technology curriculum was drawn up without consultation.

Asked in February who had advised on the programme of study he told a Westminster Education Forum event that it had been drafted internally without “an advisory structure”.

“I’m not suggesting that it was prepared, as it were, in consultation,” he said, before admitting that the DfE did not “have a body of specific design and technology expertise”.

The result takes design and technology back to the 1950s by introducing sock-darning and flower arranging at the expense of vital 21st-century technological skills, according to the Design and Technology Association.

Ministers say they are now talking to the association, which wants the curriculum to be abandoned because it is “unambitious and incoherent”, “completely inappropriate for a technologically advanced nation” and would make England the “laughing stock” of the Western world.

A DfE spokesperson said: “The draft national curriculum is challenging and ambitious. Extending the consultation period would delay implementation. A whole year of pupils would miss out on a more rigorous, knowledge-focused curriculum.”

Subject to change

ASCL concerns:

- Art and design, music: “So cursory that teachers... are at a loss to understand how this is an improvement.”

- Citizenship: “Greatly inferior to the existing programme.”

- Computing: “So technical and content heavy... it almost completely removes all the practical ICT skills that students will need for adult life.”

- Design and technology: “Return to more of a craft-based, maintenance skills approach, which will not prepare students for the real world.”

- Geography: “Too little emphasis on cultural understanding and diversity.”

- History: “Unteachable”; “will turn students away from history”.

- Languages: “Proper progression between key stages 2 and 3 will become impossible for many.”

- Physical education: “The focus on team games, rather than developing a good understanding of healthy living... is a major shortcoming.”

- English, maths and science: “Unhelpful and potentially damaging imbalance” between knowledge and its application.