Quite possibly. The idea is that there is an Optimum Currency Area, i.e. a region over which a single currency makes sense. Larger countries (including the UK

Quite possibly. The idea is that there is an Optimum Currency Area, i.e. a region over which a single currency makes sense. Larger countries (including the UK) are not necessarily Optimum Currency Areas but can mask the effects by using fiscal transfers between richer areas (or states) and poorer areas (or states). Some smaller countries do better sharing a currency even without the fiscal transfers, (such as Switzerland and Luxembourg I believe). The Euro is a classic example of far too large an area, encompassing widely disparate economies, and without sufficient balancing fiscal transfers - hence the considered opinion of many people that the Euro as it is currently constituted is not viable over a longer time period. To survive, the Euro requires one of: (a) Strong Political Union and Fiscal Transfers (b) The Departure of Weaker Economies (such as Greece) (c) Breakup, into for example a "Northern" Euro and a "Southern" Euro https://en.wikipedia.org/wiki/Optimum_currency_area https://en.wikipedia.org/wiki/Optimum_currency_area