Antibiotics are controlled in the UK to prevent their effectiveness dropping amoungst other reasons - I'm sure you know that. I'm a bit surprised you can buy amoxycillin over the counter in Spain, actually there are good arguments for moving to that here but that's another question - point is it's not a particularly good comparison because of the control.
Kew is expensive but it's hugely labour intensive and labour cost are high.
Maybe you should have gone to the National History Museum - that's
free! or the Science Museum - free too! And the British Museum.
How about an Opera? Royal Opera House errect a big screen in the summer and you can watch some of the performances on it -!
free.
The National Gallary in Trafalgar square-
free! Tate Modern on Fridays and Saturdays -!
free!.Tate Britain.
The Prado charges entrance, the Guggenheim in New York and the Uffizi in Florence are both about �10 for adults!
Rather depends what you're buying I guess!
if anybody's interested check out:
http://www.londonfreelist.com/home.asp