EDUCATION Secretary Charles Clarke is to boycott this year's National Union of Teachers' conference, escalating the dispute between the Government and Britain's largest teaching union.
It will be the first time for eight years that no minister has addressed the Easter gathering of the NUT, traditionally one of the toughest assignments in the education calendar.
Mr Clarke cited the union's refusal to sign up to last month's workload agreement, previous poor behaviour by delegates and a 10-minute limit on speeches as reasons for the boycott.
The NUT reacted angrily to the snub describing Mr Clarke's actions as "immature", but other unions said attempting to limit his speech was insulting.
Both the Conservatives and the Liberal Democrats accused Mr Clarke of "running scared" of the NUT.
And Doug McAvoy, NUT general secretary, said: "The Government talks of partnership but is willing to practise partnership only with those who meekly agree with it."
Politicians have faced a rough ride at recent NUT conferences. In 1995, then shadow education secretary David Blunkett and his guide dog Lucy, were forced into a small room for half an hour after being ambushed by Trotskyite delegates.
Subsequent conferences have seen ministers routinely heckled. In 2000, a group of teachers walked out during a speech by then school standards minister Estelle Morris.
The following year Mr McAvoy chided his members for their behaviour, telling them that they would feel better if they smiled more.
Leaders of other unions said Mr Clarke's refusal to attend the conference was a sign of the NUT's increasing isolation after its decision to reject the workload agreement.
The deal, which gives teachers guaranteed non-contact time in return for assistants taking charge of classes, is supported by the other three classroom unions and both headteachers' organisations.
John Dunford, general secretary of the Secondary Heads Association, thought it unlikely that Mr Clarke would be put off attending by NUT left-wingers.
"Charles Clarke is quite a pugnacious operator. He would enjoy a verbal exchange," he said. "It was discourteous to invite the Secretary of State to go all the way to Harrogate to speak for only 10 minutes."
His views were backed by the National Association of Headteachers and the National Association of Schoolmasters Union of Women Teachers.
David Hart, NAHT general secretary, described the limit on speaking time as "downright insulting".
Gerald Imison, joint acting general secretary of the Association of Teachers and Lecturers, said he would be "sorry if ministers are punishing the NUT" for its refusal to sign up to the workload agreement.
The 10-minute rule was agreed by last year's conference. John Bangs, NUT head of education, said: "Ministers do not go to a conference just for the speech. They use it to engage with unions, launch initiatives and talk to the press. It is a full day."
At least one senior official of another union speculated privately that the absence of the usual Easter press coverage of teachers mistreating ministers may be of benefit to the profession.