If sickness prevents a worker from taking annual leave, can the leave be carried forward?

Yes.

It is only on termination of employment that a payment can be made in lieu of holiday. If any scheduled leave coincides with sickness, a worker can designate a different time to take the holiday. The purpose of paid leave is rest and relaxation, sick leave is for recovery from illness, therefore it is not rest.

Whether leave has been merely scheduled or actually booked makes no difference, if sickness prevents annual leave, workers must be able to use annual leave at a later date if even that is in the next holiday year.