Re: US citizen going to london
Bhai sahab, I had a Pakistani passport until the age of 17. At that time I didn't really travel a lot though. And my skin colour is not really "European" either.
I know that it can be necessary to provide bank statements and stuff like that when you apply for a visa at an Embassy, but I've never heared about anyone taking along bank statements to the trip itself to show them to immigration officials.