Thanks @DartmoorDoughnut and @Delilah7! Appreciate the support.
@DartmoorDoughnut, my Mum is the same. She's so wonderful, but she doesn't like me still feeding. I know it comes from a good place of being worried about me and thinking I'd be less tired if I was feeding, but it's still hard to hear.
@TwinkleDay, it's not me in HR, but my understanding is that they can still make you redundant if you're pregnant - as long as it's not because you're pregnant. If they're using a fair and open criteria for redundancy that stands up to scrutiny, it should choose you/not choose you whether you're pregnant or not. I.e. I'm not aware that being pregnant gives you anymore protection.
If any sick leave is taken into account and you've been off for pregnancy-related sickness, that could be a reason for telling them - so that the sick leave gets officially recorded as pregnancy-related (and they can't touch you for that, even if it takes you above the amount of sick leave your policy lets you have).
But hopefully the HR expert will be along soon to confirm or deny this!
Sorry you're in this situation, it must be so stressful x