http://www.rightmove...y-32201691.html
Even if the £400 is not taking account of anything you currently pay at home, that is unquestionably going to be a whole lot less than paying Circ.£400 elsewhere....JUST IN RENT (and note the small print about fees in the ad), knowing you will have a host of utility bills on top and that's excluding food.
There is also the relationship issue with your mum to consider - you seem pretty laid back about that side of things but I suspect it is her way of introducing to you the facts of life surrounding living costs, but honestly in the SE I doubt very much you will get anywhere near the comforts of your present home elsewhere for £400 a month.
Might then leave you enough to put toward the passion we can see you have for your ZED, but if you move out it sounds like you will need all the financial help you can get from a 'parts out' to help you avoid running up the white flag in a few months time to your mum for help......or to come home.
As others are suggesting, if you do choose to move out sharing with mates or at least those who are doing the same thing (uni etc) is whole lot better than sharing with complete strangers IMO. Maybe colleagues at work might be a way forward in the sharing stakes........if you feel renting nearer work is your best option?