http://www.entitledto.co.uk/
This website is also really helpful to get some ideas but in my experience until you are at the stage that you need the help, they won't tell you how much you qualify for, which isn't helpful atall. The best i can suggest is to prepare for the worst case scenario and then enjoy your maternity leave and sort it all out upon your return or when your return is imminent.
If this helps you atall.... my husband and I both work full time and have a joint income of �35K and have a mortgage, we don't get help with childcare costs but thankfully have a childcare voucher sceme at work which is a Godsend. We get �75 p/m tax credits and �18 p/w child benefit (as everyone does).
I found it really hard not knowing what I would do when I returned to work (I only returned three weeks ago and my baby is 7months). I arranged to go back to work full time, but did condensed hours so I do 37hours over four days and my daughter is at daycare for those four days, it is only now that I am getting back into the swing of working and am able to look at my finances to see if I can afford to drop another day, but then reduced hours means reduced wages but that in turn could increase my tax credits and means I will be spending lesson childcare. It's hit and miss really and I think you have to try and make the best of the very limited help out there!