I have an offer from Cass Business School, and Tanaka Business School, Imperial College, which one should I go for? Both costing around 18k, Cass slightly more.

Do what you want mate. If one is more highly regarded by employers then maybe you should do that, otherwise go for the university that you like the look of, in terms of living in the area.

Stu... you've really gotta start taking those happy pills mate!

spend less and hope for the best as both are imperial