Abstract
The EMS's Exchange Rate Mechanism (ERM) has long been a source of political controversy, playing for instance a relevant part in the final drama of Margaret Thatcher's resignation as a serving Prime Minister. Britain entered the ERM in 1990 to exit from it in 1992 and afterward, the new Euro-politico-monetary controversy has been that of joining the future single European currency, the euro. In 1992, the Maastricht Treaty set the euro-agenda; in 1999, the euro was launched in its virtual form; and in 2002, the euro appeared in every euro-zone member's citizens' pockets as coins and notes. Joining the ERM was theoretically reversible but if Britain was to join the euro, it wouldn't be the case anymore: doing so would be violating the Rome Treaty and one can hardly imagine what unpredictable ramifications that would have. We will see in the first section what the general economical debates (I) are, I will give a brief historical overview of the EMU and expose the basic benefits and costs given before 2002. In the second section, I will give more focused economical arguments for and against entering the euro-zone regarding Gordon Brown's "five tests" (II) and more or less try to sort out economical ambiguities in the research of an "optimal currency area".
