As I read the ruling from the Court of Appeal, [i]It is worth noting that the scope for carry-over is not indefinite. Recent ECJ decisions in KHS AG v Schulte [2012] IRLR 156 and Neidel have suggested that carry-over of holiday can be limited to a specific period of time after the employee has returned to work (with 15 months being permissible and nine months too short). The Court of Appeal’s decision in Larner also expressly confirms that, once an employee has returned to work after illness, he or she will need to request to take carried-over holiday in the usual way.[i]
This would in effect, make the issue, in the case of a teacher MUST take some of the carried over leave during term-time, as not taking the accrued annual leave would be in breach of the ruling & WTD. IMO