The other two threats were from radicalized Islam and from Russian President Vladimir Putin, who Verhofstadt said was also working against the progress of the EU project.

"We have a third front, for the moment, undermining the European Union, and it is Donald Trump," Verhofstadt said in a speech at the Chatham House think-tank.

"Trump spoke very favorably of the fact that also other countries will want to break away from the European Union, and that he hoped for a disintegration of the European Union."

Verhofstadt served for nine years as prime minister of Belgium, and has served in the European Parliament since 2009.

He said that the European Union had severe problems, saying it was in a "poly-crisis", but nevertheless argued that the solution was for greater co-operation between states.