The expression "Cor blimey!", is a corruption of "God blind me!". It originated in the late 19th century, I think because the latter wasn't a very acceptable thing to sayin polite society! I suppose you'd be saying "I can't believe my eyes!".
The Oxford English Dictionary defines blimey as "used to express one's surprise, excitement, or alarm", which I think is about right; I would say primarily surprise. It is similar to other English words like cripes, gosh, golly and crikey, which I think often have similar origins - cripes and crikey are euphemisms for Christ.
Because they are polite, mild, expressions of surprise, they can sound quite old-fashioned and silly, and a lot of people would swear instead! (If they weren't in a children's book....)
This is probably more than you wanted to know... always happy to offer my services in the cause of Harry Potter! How does the French edition translate it? There must be a lot of stuff in Harry Potter that is difficult to translate...
Thanks for all this clarification, very interesting.
I don't know how they translate, I think in the movie he says "Bon sang Harry !" which is quiete old fashion too
I'm trying to read it and it's pretty difficult for me so I don't even imagine if I would translate...for the moment I just try to understand
thanks for your help !