Douglas Mackie, local EIS secretary and the union’s national president, claimed the post-McCrone agreement was being misused by the authority and warned of “a recipe for chaos in all 10 secondary schools”.

The union suspects the Scottish Executive is pressurising councils on costs, leading to vastly slimmed down structures, particularly in secondaries, where heads are said to be sceptical.

Mr Mackie said the Argyll and Bute plan, based on what the council’s “equitable formula” of one principal teacher post for every six full-time members of staff, ignored the different curriculum, staffing structure, class sizes and assessment systems in primary and secondary.

The same ratio is being applied to depute head posts with an appointment when there are more than six principal teachers.

In the secondary sector, 78 senior and assistant principal teachers would go, along with 42 principal teachers and 25 assistant heads. To counter that, the number of depute head posts will rise from 10 to 20.

The number of PT posts would drop from 15 to nine at Rothesay Academy and from 10 to five at Tarbert Academy - but only from 22 to 20 at Hermitage Academy, the largest secondary.

In the primary sector, 48 senior teachers would go but 58 new principal teacher posts will be established. The number of deputes will drop from 15 to three.

Education officials want the new structures in place by the end of May and are pressing for an early retirement scheme to ease out teachers who do not fit in. Appointments to the new posts are likely to be made in the autumn.

Archie Morton, education director, said: “These changes to the promoted post structure in schools represent the most significant alteration in over 30 years. They provide an opportunity to resolve issues of equal opportunity which have developed and they provide a clear rationale for the existence of management posts.”

Mr Mackie said the authority had no need to follow this route and warned of falling standards.

Leader, page 22