One thing I'm confused about is whether a family can get any working tax credit at all if one parent isn't working. According to the calculator I linked to above, me and hubby wouldn't be entitled to any WTC, yet hubby fulfils all the criteria. I tried it both ways, filling it in as myself first and then as him. Either way we get zilch. Bit confused about that.
Also, do you count as being on maternity leave if you're not entitled to SMP and are claiming MA instead? Obviously being on maternity leave counts as working for the purposes of WTC, so would probably make all the difference there.