Your GP will need to decide when you avail of you mat leave. If you want more time with baby I would take the mat leave 2 week before due date and then use up all holidays and public holidays afterwards.
Surely it is a matter for your employer to confirm when you can take your holidays? The maternity leave entitlements are shown here.
Taking your employer's holiday year into account it sounds as if taking your leave before your regulatory 2 weeks would be your best bet, but, as mentioned above your employer would need to agree to same presumably.
"Under the Maternity Protection (Amendment) Act 2004 at least 2 weeks have to be taken before the end of the week of your baby's expected birth and at least 4 weeks after. You can decide how you would like to take the remaining weeks. Generally, employees take 2 weeks before the birth and the remaining weeks after. If you qualify for Maternity Benefit (see below) at least 2 and no more than 16 weeks must be taken before the end of the week the baby is due"