The leader of the country’s largest heads union has mounted a damning and wide-ranging attack on government education policy, warning that schools “will not endure another year of this chaos”.

National Association of Head Teachers' general secretary Russell Hobby today called for an end to key stage one statutory assessment and for ministers to "press the pause button" on academisation.

He described primary assessment as a ‘train wreck’ and also cited recruitment problems and exam reform in a stinging condemnation of the government.

"Our patience has been taken for granted,” Mr Hobby told his association’s annual conference in Birmingham this afternoon. “There is an anger and despair in schools beyond any I have seen before.”

He used his speech to attack the government for its "constant upheaval of assessment and top down reorganisation" and called for a “fundamental review” of assessment policy.

The attack could be particularly damaging for Nicky Morgan, education secretary – who was jeered at the conference yesterday - because it comes from a moderate union leader who ministers take seriously.

Mr Hobby told delegates that the government’s changes had left assessment as "chaotic, confused, unreliable and largely meaningless"

"Changes are made at such a breakneck speed and at such volume that mistakes are inevitable," he said.

Yesterday, delegates voted for a review of assessment from the foundation stage through to secondary - and called for the government to abandon plans for year 7 resits.

Today Mr Hobby suggested a "return to the idea of a reception baseline" and a move away from "secure fit to best fit" for writing teacher assessment.

But he added: “We must ditch statutory assessment altogether at key stage one in through schools. We cannot have two high stakes tests for young children.”

"Even in the depths of our anger at our treatment, we remain constructive and positive but we will not stop until we’ve made the government see sense," Mr Hobby said.

And it is not only assessment that school leaders are angry about - yesterday headteachers voted to consider taking industrial action against forced academisation.

On the government's plans to turn all schools into academies by 2022, Mr Hobby said: "There is a reason why fifteen thousand schools have rejected academy status over many years, despite incentives and encouragement and even pressure.

"They don’t believe it is right for them. It is odd to praise professional autonomy and then reject it in practice.

He added: "I am particularly dubious of this capacity at a time of stretched budgets. These are boom times for lawyers, auditors and consultants. Better if they were boom times for teachers."

The leader called on the government to "press the pause button" and not rush through top down structural change.

“A department that cannot publish the right test paper on a website is not a department we can rely on to successfully convert fifteen thousand schools to academies in the next few years,” Mr Hobby warned. “These mistakes are not ‘human errors’ but strategic errors of pace and engagement.”

He said: "When we criticise, it is because something is genuinely wrong. The sooner politicians learn to listen, the fewer mistakes they will make."