First, the expertise and needs for both groups is quite separate and can only, sensibly, be served by professionals with backgrounds in each speciality.
The implied second position is a "super" union for teachers. This would be a disaster for two reasons. In the first place it would allow the Far Left to exercise influence in a far more effective way than in National Union of Teachers' affairs.
Second, the sharp edge of competition between the three main unions would be lost. Society enjoys and profits from the rivalry between supermarkets. Teachers, if they are sensible, will ensure the same advantages.
Peter Shirley 35 West Street Chipping Norton, Oxfordshire