Charles Clarke will today launch a strong attack on the "posturing and sloganising" of the National Union of Teachers.

The education secretary will use a speech to the National Association of Schoolmasters Union of Women Teachers conference to say that its "annual antics" harm the reputation of the profession.

"Let me tell you why I did not go to the NUT conference," he will say. "In my view nothing does more to depress the reputation and standing of teachers than to witness the annual antics that go on there.

"Posturing and sloganising at its worst. And parents and the public think: 'Are these the people that teach our children?'. Teachers are held in high esteem - but they will forfeit that esteem if they start back down the path of strikes, boycotts and sending children home."