U.K. mums - maternity leave

Hi, I'm asking UK mums specifically, because I know the allowances are different, which may impact people's decisions. 
I'm trying to decide when to leave work, I plan to start my maternity on my due date, but have up to 5 weeks holiday to either take before I go or carry over to the end of my maternity. I plan to have the full year maternity leave.
This is my first, so I don't know how I'll feel further along (currently 22 weeks) but need to give my employer my leave date soon. 
I know I should try and save as much as I can for when the baby is here, and don't want to waste my holiday just waiting for her to arrive, but I hate my job and can't wait to leave! 
When is everyone else leaving?