The leaders of the rival camps in Scotland's upcoming referendum on independence clashed Monday in a second televised debate that again highlighted a heated disagreement in the U.K. over which currency an independent Scotland would use.

Alex Salmond, leader of the pro-independence Scottish National Party, said that in the event of a vote for independence in the historic poll Sept. 18, he would seek to negotiate a formal currency union with the remainder of Britain—an arrangement opposed by all three of the U.K.'s major political...