Primary headteachers who are demanding to be put on the same pay scale as secondary heads are to launch a formal grievance against a local authority within six weeks.

The complaint could end in an industrial tribunal and a renewed attempt by a union to use equal pay legislation to address teacher grievances. Should the Scots heads win, it could cost millions of pounds in higher salaries and lead to knock-on claims throughout Britain.

The Association of Head Teachers in Scotland has confirmed plans to launch a test case, despite last week’s equal pay defeat in the Lords for the Scottish Secondary Teachers’ Association (page four).

The SSTA failed to convince the Law Lords there was any sex discrimination involved in the former Strathclyde Region’s decision not to pay nine women teachers the salary of a principal teacher. The women had taken on added duties in new departments, such as computing, but were never paid extra.

But Jim Smith, the AHTS’s secretary, said the verdict would have little impact on the heads’ case, which has been in the pipeline for more than a year. “The SSTA defeat should not affect us. Ours is a different case and we are making it on different lines,” Mr Smith said. He believes precedent is in the association’s favour. “Primary class teachers are paid on the same scale as secondary teachers. The contract and hours of work are the same. That should simply be extended to headteachers. There are one or two avenues we can take and we are working on that.”

The association is likely to argue for pay parity on grounds of equal value, rather than the like work argument that the SSTA relied on. It wants all heads of primaries and secondaries to be placed on the same scale and for the school roll to be the sole criterion for pay levels.

Primary heads that mount a test challenge will use neighbouring secondaries as a comparison. The Equal Opportunities Commission is lending support but, so far, no financial backing after heavily supporting the SSTA. The costs in that case ran to well over pound;100,000.

Mr Smith said: “It would still mean secondary heads would be paid more because they have got bigger schools. But it could mean most primary heads would get an increase and in some cases it would be substantial. You are talking about several million pounds more and that could be the trouble for the Government.”

The association believes the Scottish Joint Negotiating Committee could have rectified the differential but failed to act.

Primary heads are almost certain to claim sex discrimination, the key test under equal pay legislation, as the Lords identified. More than 90 per cent of primary staff are women but a little over 70 per cent are heads. Men are therefore disproportionately represented.