Thanks High Dyke for the comprehensive answer. Much appreciated.Basically, give the roster clerk as much notice as possible in that calendar year. If it means booking leave then don't wait until a few weeks before otherwise you may be disappointed, especially if you have already paid for an event. Most roster clerks will try and accommodate a leave request where possible. If it's short notice leave you require then that needs to be sanctioned by your line manager; it may be that the quota for your area has been reached.
You are able to carry over up to 5 days, but you must have applied for them in the year accrued and had them declined to do this. The days must be taken by March of the following year, or they will be lost. (* See below)
Compensatory Leave (accrued for Bank Holidays, if you choose the lower pay option). They have a 12 month date on them, after which you get paid them.
* Days accrued in 2020 need to be applied for by December 31st 2020, and declined by your roster clerk/manager. Those days must then be taken by the end of March 2021.