She told the second biggest teaching union last week that industrial action was inexcusable and that strikes by teachers were not in the best interests of children.

Her message to the National Association of Schoolmasters Union of Women Teachers’ annual conference in Bournemouth last week came as teachers threatened to take industrial action at a Yorkshire school.

The dispute is the latest in a growing list of controversies in which teachers have been balloted on strike action after being forced to teach allegedly violent or disruptive pupils.

Last year, the NASUWT was involved in four major disputes at Hebburn comprehensive in South Tyneside, Glaisdale in Nottingham, Manton junior school in Nottinghamshire and The Ridings school in Halifax.

The dispute at Hebburn, almost a year ago, is still not resolved. Parents have applied for a judicial review over the rturn of the pupil -Graham Cram - and legal proceedings are ongoing.

With growing concern among classroom teachers about disruptive behaviour, the NASUWT has taken a lead in using the strike weapon to force schools and local education authorities to exclude pupils who misbehave.

Mrs Shephard told the 500 delegates to the annual conference: “Whatever the situation in a school may be, there is never any excuse for a professional person to strike or to take industrial action.”

She was heckled as she went on: “It is not the way for professional people to behave, and for teachers the interests of the children should always come first. They cannot be well served by absent teachers.”

Mrs Shephard said proposals in the Conservative manifesto would give people a legal avenue to prevent public-sector strikes - and said parents would be able to use the provision against teachers.

Before the conference she told journalists: “Proposals in our manifesto make it possible for people disaffected by public-sector strikes to bring an injunction against them.

“I cannot conceive any circumstances which would justify teachers going on strike and, in any case, to deprive children of their education is not a professional act.”

Mrs Shephard claimed that had such a provision been available during the disputes at Manton and The Ridings schools staff would have had to “think twice” about their action.

But Nigel de Gruchy, general secretary of the NASUWT, said staff at those two schools would have walked out anyway and said: “So be it.”

He told Mrs Shephard that the Conservative party’s proposals struck at the heart of democracy and human freedom, and added: “Those questions should be left to people to decide for themselves.

“We take a very serious and deep objection to what is a dirty, backdoor method being proposed in the Conservative manifesto to make it impossible for people to act on their own.”