Employees are legally entitled to reclassify holiday/the balance of a holiday during which they become ill as sick leave, and are also entitled to do so where they become ill before a period of booked holiday so that their sick leave would coincide with their holiday. (This is based on case law which establishes that the purpose of annual leave (rest and relaxation) is different from and incompatible with the purpose of sick leave (recovery from illness).) This entitlement applies only to holiday that is part of the 4 weeks minimum annual leave under the Working Time Directive (WTD). However, it can be difficult to distinguish the WTD part of an employee’s holiday, and there can be other administrative difficulties, so employers often apply these and other principles relating to the interaction of holiday and sickness to all of an employee’s holiday entitlement.