Thank you everyone, it does really help to know I'm not alone.
You're absolutely right that supportive line management makes all the difference. Unfortunately I think my line manager has been largely responsible in causing my current depressive episode, as he was very horrible and unsupportive in dealing with the physical health problems I've had over the past year. Given his attitude toward this, I can't come clean about my mental health problems. The occupational health doctor I saw agreed with my instinct not to do so.
But if I am subjected to a capability assessment - is it enough that I've told Occie Health?
I've told my colleagues (all 3 of them, it's a tiny team and we're all very involved in each other's work), including my immediate supervisor about it, but have been shocked by their response. My supervisor told me (when I broke down in tears) that she worried what was "so wrong" with me that I couldn't deal with things, and I had "to reflect" on why I was getting so upset. Another colleague told me it was my problem that I couldn't shake off my boss's behaviour and all I needed was thicker skin.
It feels like a bit of a betrayal that I opened up to them and they blame everything on me being "oversensitive". They knew me before this depression hit when I was coping and saw the change - but think it's my fault things degenerated, and don't acknowledge the burden of mental illness.
And movingtables - hang in there. It's horrible and being alone and isolated at work and not good for us depressives. Can you change your shifts to be around people more? I know that I don't paint a good picture of being in a team, but TomCrick and Willows have some much more positive stories.