The easiest place to institute capital controls is the border of the European Economic Area (single market).

Otherwise, the Hungarian Central Bank might have been inclined to put a stop to Hungarian banks offering people loans denominated in Euros or Swiss francs, but that would have been instituting capital controls within the single market and couldn't be done. All they could do is lean on the banks to restrain themselves voluntarily.

Most economists teach a theoretical framework that has been shown to be fundamentally useless. -- James K. Galbraith