Sorry Giraffe, I still don't quite understand. You said earlier that you had worked for your employer since October 2007. If your sick leave also started then, does that mean you've never worked for them actively?
In terms of the maternity leave period, if you were off sick for 10 months before you went off, then took the full year of maternity leave without explaining why you thought that you were forced to, I think you may struggle to convince a tribunal that you would otherwise have returned sooner and should be compensated for that time.
The loss of earnings from Oct 2007 to July 2008 is the key bit. What's their offer compared to what you'd have earned in that period (net earnings) as a rough percentage. It's hard to say how likely you would be to be successful in your claim without knowing a lot more about your illness, your expert reports and what you wanted your employer to do. The tribunal will have to be clear that you'd have been able to go back if the employer had made the adjustments. They will also have to be convinced that the adjustments you asked for were reasonable. Bit beyond the scope of this board. However, this is the key bit.
I'm sorry to say it, and you probably know, but you didn't help yourself by not explaining your absence or responding (or getting your mum to respond) to the letters.I don't quite understand why your doctor stopped signing sick notes. Either you were fit for work or you weren't. They should take the job as the find it. Did the doctor write to your employer to explain what could be done to allow you to return to work?
In terms of injury to feelings, again hard to say, but your solicitor is probably right. Injury to feelings awards are based roughly around some guidelines to do with the behaviour, not necessarily totally the impact on you. £5,000 is the middle band of award. Higher awards (£5,000 to £25,000) are normally reserved for more sustained programmes of active harassment. Your employer, from what I can see, didn't implement some adjustments that you say were reasonable. They also had an internal communication failure which meant you were called to a disciplinary when you didn't return after maternity leave/holiday without submitting a sick note. Yes, it's bad that they didn't talk to OH, but it wasn't malicious, you were absent without authority (and could have had your mum tell them about the OH conversation), so I don't think that that bit would bump up you injury to feelings award. [that doesn't mean sacking you was fair by the way, just that I don't think it adds to this bit of any award]. That means that he only injury to feelings bit is really the not implementing adjustments, and that's very much a low/middle bad infringement, not something you'd expect to go over £5,000 for (IMO).
Hope that helps a bit. Have you got the cover solicitor to write requesting an extension to your deadline?