I think most people get the last 3 months unpaid unless their work offers an enhanced mat pay for those months, which I don't think many do. I'll be going back after 9 months too because we can't afford to be on one salary for 3 months, after the previous 3 months just SMP.
The system is definitely backwards! Don't get me started on benefits... I think it's a great idea to have benefits to help those who really do need it. But I know quite a lot of people who don't even consider having a job, choose to live on benefits, have a few kids, and end up "earning" almost as much as me through benefits, and on top of that they get free childcare too? It's unfair when some people take advantage of the system.
But yes I forgot about childcare help we get. My work does "childcare vouchers", which basically means they take some of the childcare costs out of your salary before tax, so you're essentially getting to pay some of it tax free. But you have to place them with a registered nursery or childminder to get that.
Also, don't forget you still accrue holidays while on mat leave, and some work places allow you to take all your holidays at once after your maternity leave. So you could basically end up with an extra month or whatever at full pay. I'm trying to get that, but I'd be returning from mat leave just after our holiday year is over and the HR manager doesn't allow people to carry over holidays... hoping my manager overrules her (as he usually does) and allows it!