Based on what you've said about dates, you should still be eligible to receive statutory maternity pay from your employer - based on your due date, your qualifying week is the week starting 25th November 2012.
Briefly, you have to inform your employer of your pregnancy by the qualifying week. Assuming you earn more than £107 per week, if you were employed by them before you got pregnant, worked for them continuously (you still count as employed while on holiday / sick) throughout your pregnancy, and are still working for them during the qualifying week, then they legally have to pay you SMP.
This is true even if you're made redundant after the qualifying week.
So, if you stay employed until 31st December, that's past your qualifying week, so therefore your employer legally has to pay you SMP.
Employers can legally make pregnant women redundant, so long as the redundancy isn't related to the pregnancy.
Hope that helps. And congratulations on your pregnancy