Charles Clarke has launched a fierce attack on the "posturing and sloganising" of the country's biggest teaching union.

Facing a growing crisis in relations with the powerful teaching unions, the education secretary lived up to his reputation as a "bruiser" when he delivered a keynote address at the NASUWT conference.

He also defended his department's record on funding schools, in the face of criticism that it has left heads having to make budget cuts at a time of spending increases.

Signalling an unwillingness to countenance compromise with his critics in the NUT, Clarke slammed the union's refusal to sign up to an agreement on teacher workloads and classroom practices.

The reform deal, agreed after months of negotiations, has already been backed by ministers and local authorities.

The NASUWT gave its formal approval to the move on Thursday morning.

Having snubbed the NUT with a refusal to attend its Harrogate conference, Clarke rubbed salt in the wound by praising the NASUWT's members for their support.

In his first address to a major teaching conference since taking the job last year, Clarke couched his remarks with continued references to teachers being "professionals".

But he warned the militant elements within the NUT that "professionals need to act and conduct themselves in a professional manner".

"A professional has the confidence to know and value the support that other members of a team can bring," he claimed.

"I want to engage in serious dialogue and to uphold and enhance the reputation of teachers and not denigrate it."

"Teachers are rightly held in high esteem, but I believe they will forfeit that esteem if they start back down the path of strikes, boycotts and sending children home."

He warned the NUT that "nothing does more to depress the reputation and standing of teachers than to witness the annual antics" of its conference.

"It is posturing and sloganising at its worst. The sort of performance that the House of Commons or party conference never comes close to matching, even on a bad day."

Addressing NUT delegates earlier this week, general secretary Doug McAvoy launched a blistering attack on the government.

He condemned the minister's "sinister, totalitarian, anti-democratic and McCarthyite" tactics.

Tensions grew after the union voted for strike action over a massive expansion of classroom assistants, saying only fully qualified teachers should be left in charge of pupils.

Delegates at the union's annual conference also backed proposals to limit class sizes to 27 by sending pupils home on a rotational basis.

NUT members are also set to vote on a boycott of national curriculum tests.

Clarke mounted a strong defence of the use of targets and tests in measuring progress towards meeting performance ambitions and vowed that tests for seven, 11 and 14-year-olds are "here to stay".

He insisted that tests were not the "be all and end all of teaching or going to school".

But he added that targets were used throughout all professions and that "teaching should not be an exception".

"Goals and targets set a standard. They show us what needs to be achieved," he said, insisting that tests were the only way of measuring this.

"When politicians come along and say: 'Away with the tests and away with targets' then I have to say that they are living in Alice's Wonderland."

And he entered the debate on unruly pupils who unions complain have been allowed back into the classroom, against the interests of teachers and pupils.

Appeals panels have controversially reinstated pupils in a number of high profile cases.

"Appeals panels have been given the responsibility to balance the interests of the excluded pupil against the interests of the rest of school community," he said.

"They cannot reinstate a pupil just on a technicality."