Local authorities are trying to decimate the promoted post structure in secondaries, leaving schools “almost unmanageable”, David Eaglesham, SSTA general secretary, cautioned.

Alan McKenzie, the union’s president, said that so far principal teachers had successfully delivered everything that had been thrown at them - including Standard grade and Higher Still, social inclusion, the Scottish Qualifications Authority fiasco, anti-bullying, computer literacy, differentiation.

“The list is interminable. Then they turn and say the system is not flexible enough. I don’t know how bloody flexible they want the system,” Mr McKenzie said John Gray, Aberdeen, said that the aim of the authorities was to “restructure, reduce and remove” without providing any justification.