Take Eurostar from London to Paris - if you are under 26 u can get the youth fare for $123 canadian as of July 1. Then get a connection on to Barcelona. Check out: http://www.eurorail.com/
I had a Eurorail pass for 5 countries and had 11 different connections or something like that, for around $500 canadian. Super good deal considering half my trips they didnt even punch my ticket!
so i used many more connections. Remember all youth fares if you are under 26 - very cheap!
Oh just found it costs almost $200 canadian from Paris ro Barcelona individual fare but they only had adult quote. Check Eurorail pass for sure, then you can visit many other places and also not limit yourself to one country.