Oh dear. This is a common scenario for the younger job seekers of today. Have you tried to see if you are entitled to any help such as housing benefit or a crisis loan, bridging loan or other grant. It might be worthwhile speaking with citizens advice as they may be able to offer you help and advce about the situation.
Have you even actually been offered this job? If they are just pushing you to take the interview then do it, and if you dont think the job is for you then explain in the interview that you like the idea of the role but you really dont think you are suitable due to the travelling distance etc. 12 miles isnt excessive if you drive, but if youre having to go under your own steam im sure it will be! And what about bad weather, when its snowy and you cant get in. No job is worth risking your life for.
So in short, I would advise turning the job down if it is going to make your life difficult, but advise A4E that you would have loved the job had it been closer. You could try approaching local gyms yourself and seeking employment with them.