I'm currently on a leave of absence for depression, between my first and second years of undergraduate study. The biggest financial issue for me was paying council tax, which came to almost £900, so it's definitely something you'll have to look into even if you change to part time study. Luckily I did have savings so I'm going to be able to make it through this year, but it sounds like you might need to get a job during a leave of absence to cover your expenses, which might not be feasible depending on the nature/severity of your depression.
For me, taking a leave of absence has been really useful so far because I've been able to take things at my own pace (a lot of my issues were triggered by stress, so removing the second biggest stressor in my life was a good step to take). But it sounds like there might be a lot of financial complications for you, and if you don't have a good plan of what you want to do in your time out then you could end up just being directionless and lethargic, which could make your depression and anxiety worse.
I've found Student Finance singularly unhelpful with all of this, but your tutor might be able to give you more information about the financial consequences of a leave of absence, and if your uni has a counselling service I'd advise seeing someone to discuss the other options you might be able to take instead of taking time out from study.
I think that's all I have to say - sounds like Higgs is much better qualified to answer your questions, but I just wanted to put my two pennies in ( :