I'm in the lucky position of having a free afternoon in London. My hotel is down the road from the Natural History Museum - does that make it Kensington?
I need some nice, but not too expensive tops and a work dress or two (fairly casual work environment but needs to be reasonably smart).
Where can I go to best effect? I don't want to spend hours schlepping across town and I also don't know London at all so if you have a suggestion please be as clear as poss as to where it is/Street name/nearest tube. 
I intend to spend a couple of hours in the Nat Hist Museum as well so shops the more local the better.
Thanks! 