If you wear a tie, you're likely to be in a small minority on a Saturday. If you go during the week and you see people dressed in suits, it'll only be because they've gone straight from work.
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by USAFAN:
I agree. I went to the Royal Symphony Hall (or so, on the other side of the Thames), and all/most people where very casually dressed.</font>
Exactly. The same goes for concerts, too. I think you were probably at the Royal Festival Hall.