Cashing in leave
You can swap up to 1 week of your annual leave for cash each year — up to 5 days if you work a regular 5-day week, or one quarter of your annual entitlement if you don't.
Ask your employer for this in writing.
You can ask to cash in leave multiple times a year, as long as the total you cash in isn't more than a quarter of your total leave allowance for the year.
Leaving a job
The only other time you'll get cash for your leave is when you leave your job — your employer will pay you out for any leave you've earned and haven't taken.