@Sophie thank you!
https://www.gov.uk/calculate-your-holiday-entitlement
I am not sure but where I work you do not accrue holidays or vacation when on mat leave. I only got holidays/vacation for the time I was actively working
Divide your yearly allowance by 12. That’s how many days you accrue each month. So if you’re entitled to 24 days holiday (+bh) you’d be entitled to 2 days per month + bh if it falls in that month.