You can also still get maternity allowance whilst you're working as it's paid regardless. This is what happened to me when I was pregnant with d/d before. Hope it helps.
From what I've read this isn't true and I don't know how you managed it!
You can work 10 'Keeping in touch days' but any more than that and your MA is affected. MA starts when you finish work and stops at 39 weeks or when you start work again, whichever is earlier.