That's a hard one to explain, Sergio. Generally, copyrights are international, although the U.S. Congress unilaterally extended copyrights to something like 120 years (most songs published before 1923 are in the public domain, and songs published after that can go up to 120 years. Performing in a not-for-profit situation is generally exempted from the requirement to pay royalties (fees) for use of a song - but apparently the pubs in Great Britain may have to pay fees if they allow their patrons to sing.
-Joe Offer-