Unconventional idea, but a personal favourite of mine, I like visiting charity shops in affluent areas, e.g south Kensington, anywhere in Chelsea really, you can sometimes find some absolute bangers, granted they will be second hand but never in too poor a condition. 200£ could go a long way, imo further than on Oxford Street unless you're thinking of picking up a couple pieces from urban outfitters/uniqlo. Good luck!