P111 CJJFAX 111 Tue 19 Vun 20:33/32       A teachjrsg union has accused Education Secretary Sir Keith Joseph of trying to prejudice the decision of possible arbitrators in the teaching pay dispute The attack follows a Commons statement bz Sit Keith, in which he said no more money was available even if the dispute went to arbitration. NUT general secrjtarz Mr Doug McAvoy said he was trying to nobble arbitrators even before thieu work had started. Sir Keith said the teachjtsg action was causing immense damage to school- children.