She was expected to praise delegates at the Association of Teachers and Lecturers conference in Torquay for their professionalism and the constructive relationship the union has had with the Government on workforce reform. She said her aim to create a society based on social justice would not be possible without the input of education.

But Mrs Kelly, who had already endured a scornful response when she spoke to the Secondary Heads Association earlier this month, faced a union which, though traditionally moderate, had voted on a number of motions criticising her policies.

Delegates voted unanimously for the ATL to “take all possible steps” to persuade ministers not to go ahead with its plan to create 200 academies, and make every secondary a foundation school.

Phil Baker, Swindon branch secretary, said academies “appeared to be a Trojan horse designed to destroy the teaching profession”. He said: “Why else do they seek to do away with national pay and conditions?”

Mary Bousted, the union’s general secretary, was expected to use her speech to condemn the Government’s numeracy and literacy strategies, calling them “the final nail in the coffin for teacher autonomy”.

She was to argue that it was treating teachers as technicians rather than professionals. In an interview with The TES she called on ministers to conduct a radical review of both strategies.

The conference was told of a survey showing 72 per cent of secondary teachers had considered leaving the profession because of disruptive behaviour. Bad behaviour had led to 46 per cent suffering stress or other mental health problems and 14 per cent had been physically harmed, according to the survey of 300 secondary staff, conducted this month.

Elizabeth Greed, an English and RE teacher from Wiltshire, revealed that she had been threatened with a knife and had to disarm a pupil who had brought a loaded handgun into school. She blamed the decline in behaviour on a lack of respect from parents and drugs. Pupils, she said, were taking horse tranquillisers and smelt of “wacky baccy” when they came into school.

Delegates passed a motion supporting school trips and calling for local authorities to continue to fund residential and training centres. But they want the Government to protect staff from being sued by introducing a “no-fault compensation scheme” to cover serious injuries or fatalities on trips.

Motions calling for better pay for support staff and condemning suggestions that teachers should help with homework in the evening via e-mail and text message were also passed.

Delegates were expected to call for the end of key stage 3 national tests.

Iain Freeland, from Challenge College, Bradford, who called for their abolition, said there had been a “spiralling deterioration” in the quality of the tests. He said his school had to send back 40 per cent of its English KS3 test papers last year because of faulty marking and did not get its results until October.

Extended schools also came in for criticism. Ralph Surman, deputy head of Cantrell primary, Nottingham, said they would make schools responsible for every facet of childcare.

“Potty-training, care, table manners, meals, social skills, drug-testing, before and after-school care and contraception advice become the responsibility of someone else other than parents,” he was expected to say.