Sections 19 and 20 of the Organisation of Working Time Act 1997 govern the entitlement of employees to accrue annual leave while they are on certified sick leave and to carry that leave forward from one leave year to the next in certain circumstances. In summary, an employee on certified sick leave continues to accrue annual leave and if, by reason of their illness, they are unable to take that accrued leave in the leave year, they can carry the leave forward to be used within 15 months of the end of the leave year.

It is important to note that the Organisation of Working Time Act 1997 only provides for the accrual and carryover of statutory leave, and not contractual leave in excess of an employee's statutory entitlement. Furthermore, employers are often unaware that the statutory leave year runs from 1 April to 31 March and this is the relevant leave year when it comes to determining entitlements under the Organisation of Working Time Act 1997, irrespective of whether that aligns with the employer's leave year. Finally, employers should be aware that accrued but untaken annual leave is carried over on a "use it or lose it" basis and, therefore, if the leave carried forward has not been used by the expiry of the 15-month carryover period, it is forfeited.