Read tbe NHS maternity policy - it'll be on your intranet usually. Plus I believe you manager sits and goes through what you're entitled to anyway. Be careful of qny leave you take; I seem to recall something about if you take leave the following financial year to your current annual leave entitlement then you would have to pay it back - not sure how accurate that is.
I think to take the full years leave you get a certain amount of months on full pay, then another alloted amount on half pay and then when that time is up you either use annual leave or you have unpaid leave. Again, check your policy, I may well be confused as I've only hadto help work it out for one staff member.