I don't know! I certainly felt awkward. The guy conducting the interview was wearing jeans and a shirt with open collar and his boss jeans, shirt with open collar and a hideous jumper. Would have felt more relaxed, probably.
I did go into a department store to see if I could find a black jacket. A very lovely woman came to ask if I needed help and, after taking me to the window to look at me in day light, sent me packing saying I looked perfectly fine and didn't need to buy anything!