with the abundance of students in sheffield I think this is the best market to target. I think your most viable option is fashion. high street brand clothing such as bench, quiksilver, mambo, drunken monkey, even prada and gucci are easily availiable from wholesalers and distribution companies for upto 90% off retail value. Also fashion retail is the fastest growing market in the north of england. even if you purchase stock direct from the manufacters' you will make a tidy profit.
An independant fashion retailer near my place has been open for less than two years and has gone from a single retail unit to a double, also he's gone from owning a ford mondeo to owning a brand new bmw x5, thats a £40000 car so he must be doing something right.