In the absence of EMU, the 2007/2008 financial crisis would have brought such a system under severe pressure, as doubts about the liquidity and solvency of specific banks would have combined with a drying up of funding in the interbank and foreign exchange markets, concerns about government budgets and doubts about the willingness to defend fixed exchange rates in particular if this meant raising official interest rates in the face of economic slowdown.
The experience of Denmark, an EU country that has opted out of the common currency, provides a glimpse on what could have happened. While the fundamentals of the Danish economy and banking system were no particular source of concern, the Danish currency came under pressure when the financial crisis intensified in September 2008 (Danmarks Nationalbank 2008).