Currency Exchange - Bang Na Or Seacon Square Area

I'll be passing through Bangkok soon with a friend and we'll just be staying for two nights in Bang Na before going north. Because of flight times we only really have a day free, which we planned to split between shopping in Central and Seacon Square. My friend wants to change some British 50 pound notes and to take advantage of the slightly better rates some money changers will give on the bigger notes. I don't want to have to go into the city for SuperRich or similar, but know that the banks don't give any more for large notes. Does anybody know any bureau de change (or gold shops etc) that do in this area? If you feel moved to comment on my Scottish antecedents, please don't bother.

Edited July 17, 201213 yr by citizen33