Controversial issues: guidance for schools.
5. To what extent is it legitimate for teachers to take part in protest?
Some teachers may feel pressure from their head teacher or school governors not to be seen supporting partisan views outside school, e.g., by leafleting, going on marches, etc. School managers have no right to exert this kind of pressure on teachers.
Teachers are citizens, too. They have a right to hold opinions on matters of public policy, and a right to have their opinions heard. They are perfectly free to go on political demonstrations or take part in campaigns - so long as it is in their spare time.
Teacher action during contracted time is a different matter.
As has already been noted, the promotion of partisan political views within school is against the law. This may include the wearing of anti- (or pro-) war badges, and is likely to include encouraging pupils to take part (or not take part) in externally organised demonstrations. The impact of the recent Human Rights Act in this area has not been tested. The prohibition on promoting partisan political views will have to be balanced against the right of freedom of expression.
Teachers who, regardless of the law, feel they have a moral obligation to promote their personal views in school must be prepared to take the consequences. Where someone finds the moral stance they take on an issue is incompatible with their obligations as a teacher, they may wish to consider resignation. In any case, such a state of affairs could lead to disciplinary action.