I have been going to the post office at Charing Cross. It's easier for me cause I live so near London Bridge and kinda door to door from stn to stn by train in 10 mins. The queques long and customer service in London Bridge very slow and am too lazy to walk all the way down to the other end of BHS. Charing Cross has over 10 counters and despite the queques, it's really quick. Then it's to soho or chinatown for some good food.
Gosh, sledge hammers and nuts come to mind...a TUBE journey to the Post Office for heaven's sake, things are getting ridiculous. I did indeed try getting into the Walworth Road the other day - but fled in horror. So I'll buy my stamps at the corner shop and put a day aside if I need anything Post Office related.