Oh hurrah, I got a comment from FabbyChic! 
First of all gallifrey, I am very sorry to hear about your situation, that's really tough. I must confess I thought that being signed off sick still made you an employee, so I take it SSP doesn't count as earnings? These things can get so complicated. I truly hope you can get MA (and at least it's not taxable then, I believe?)
I haven't been off sick for 9 months coco, it's been 5 months. And I haven't been living off SSP as such, I absolutely would not been able to pay my share without using a small amount of savings I had, selling things, and a bit of help from my mum. I put all of this in the pot and have made it last somehow in addition to DPs wages. And now he's without a job.
Nowhere in my contract or our HR policy does it state anything about the qualifying weeks, only the number of weeks you must be an employee to qualify for SMP. As I'd been there for 8 years I knew I was covered in that aspect. I did look on Directgov but did not spot the qualifying weeks part. There is a lot of information out there.
As I have explained, my mental health has been very fragile - it took me months to even be able to think about work and what to do. Any contact with them triggered panic attacks, insomnia, not eating, and I found it hard not to cry all the time. I also had two major family issues to deal with including a bereavement in December. So my "advice/practical" head hasn't always been the strongest.
But this is not the point - I asked whether it was fair - and I still maintain it's not. Clearly it isn't, if some people can boost their earnings specifically during those weeks, and others are penalised for being ill. If I had been given the correct management and support in advance from my manager and my work, I wouldn't have burned out (again) and wouldn't be in this position. And now I am too worn out from the battle (and they know this) to challenge it. And I want to be careful because I know it will make me ill again.
I'll check with my union rep, just in case there is any case for special circumstances of being off sick, but I'm not holding out much hope. HR are the ones who sent me my maternity letter so I know the calculations have come direct from them.
Just feels like a kick in the teeth after 8 years of working extremely hard. Just because they are doing their legal requirement doesn't make it morally right. But I suppose I shouldn't be surprised, given their past actions.