Best place to get pounds for dollars

[tr7v8]

I have around $10k which I need to get into sterling, any suggestions as to the best place? Post Offices seem to do a good rate most of the time.

[Maxf]

I used Thomas Exchange in London last time - they seemed to be the best rate I could get for cash. I think the exchange rate was 1.6 while they paid 1.58 - compared to the post office being something like 1.55.