Fresh turmoil in the European Union risks triggering the disintegration of the entire bloc, according to Moody's.

In a stark warning, the rating agency said the "painful adjustment" faced by some countries in the eurozone meant the collapse of the single currency area and wider EU was believed by some to be a question of "when" not "if".

Moody's said that even a "small crisis" threatened to set off an uncontrollable chain of events that would "threaten the sustainability" of the EU and its institutions.