The Danish referendum under which they joined the EU, specifically said they would stay out of the single currency. (Maintaining control of their own monetary policy.)
In 1993, Danish voters approved a revised EU treaty, allowing Denmark to stay outside a single EU currency.I wouldn't count on it. Changing the rules without bothering to ask the people if they approve is SOP of the Brussels crowd these days. (Democracy is so untidy.)
Helle Thorning-Schmidt says the waiver "must be respected,"