An excessive accrual is more than 8 weeks (10 for shiftworkers). After genuine attempts to agree, the employer may direct leave in writing only within the limits (no balance below 6 weeks, periods of at least a week, starting 8 weeks to 12 months ahead, consistent with agreed arrangements), and an employee with an excessive accrual for over 6 months may by written notice require leave within the same limits (up to 4 weeks, or 5 for shiftworkers, in 12 months), which the employer must grant.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.