I would get the rep to point out this part of the way forward agreement to your dom:
Selection of annual leave
The objective will be as far as possible to maximise leave opportunities for employees, whilst ensuring that operational needs and the customer specification are met at all times. This agreement covers selection of full week leave and part week e.g. holidays staring mid-week. Single days leave will be agreed locally through the Staff Resourcing Manager in Mail Centres or the line manager in other operational units.
The leave year will be April to March. The Christmas pressure period, determined by the operational unit, will be a closed period for leave.
The selection process should be complete by the end of the preceding October each year.