I've learned something quite crucial, and thought I should share it
I'm self-employed, and don't make very much. I held a 'small earnings exception certificate' until a few months ago. I also voluntarily pay Class 2 national insurance and always have, even though I'm not required to.
However, even if you're paying your full Class 2, if you have a 'small earnings exception certificate', you are NOT ENTITLED TO FULL MATERNITY ALLOWANCE.
There is time to correct this if you're not very far along, as you need to pay Class 2 (without the certificate) for 15 weeks to qualify for full maternity allowance. But I could see this completely buggering up some people's plans if they don't realise they're not okay, even though they're paying Class 2. It's the difference between £30 a week and £140 a week (roughly) so, real money.
I hope maybe this helps someone. I find it bonkers.