George Soros has accused the Hungarian prime minister Viktor Orbán of building a “mafia state”, as he warned the fate of the Central European University he founded still hangs in the balance.

The Hungarian-born financier and philanthropist said he was confident the university’s defence of its freedom would ultimately “bring the slow-moving wheels of justice into motion”, but said it and other organisations he had backed were still at risk under the Orbán-led government.

Hungary’s populist prime minister has introduced tough measures for the registration of foreign-registered universities that could force the closure of the CEU, one of the top academies in the region. Thousands of people protested in Budapest in April against a bill seen by many as targeting the university.

In a wide-ranging speech on European integration, where he recalled how his Jewish family fled the Nazi occupation of Hungary, Soros hit back at Orbán for casting him as a scheming “currency speculator” in an “unrelenting propaganda campaign”.

“This is not who I am. I am the proud founder of the Central European University.”

Soros said he was “full of admiration for the courageous way the Hungarian people have resisted the deception and corruption of the mafia state the Orbán regime has established”.

Earlier in the speech, he defined a mafia state as one that maintained the facade of democracy, while rulers used the media and judiciary to enrich and keep themselves in power.

Speaking to a Brussels audience, Soros called for a radical reinvention of the EU to overcome the bloc’s “existential crisis”. He painted a vivid picture of the problems gnawing at the EU’s foundations, from the “dysfunctional” eurozone that had led to imposed austerity on debtors, to hostile neighbours and unreliable allies.

“Externally, the EU is surrounded by hostile powers – [Vladimir] Putin’s Russia, [Recep Tayyip] Erdoğan’s Turkey, [Abdel-Fatah al-] Sisi’s Egypt and the America that [Donald] Trump would like to create if he could, but can’t.”

But the “biggest threat” in Soros’s view is “the danger of a banking and migration crisis in Italy”. Italy’s government, which could face early elections, is struggling to deal with thousands of migrants crossing the Mediterranean sea, as well as the unsolved problem of Italian banks weighed down by bad loans.

Soros also predicted that Britain’s EU divorce could take five years and “will be an immensely damaging process, harmful to both sides”. But the man who once bet and won against the Bank of England, said a British vote to rejoin the EU could not be ruled out.

He urged the bloc not to punish Britain, but to use Brexit as a catalyst for far-reaching reforms, a process he thinks could help trigger a vote to rejoin the EU. “This seems practically inconceivable right now, but in reality, it is quite attainable.”

Despite the daunting list of crises, Soros said there was momentum to change Europe for the better, citing setbacks for the anti-EU populists Geert Wilders in the Netherlands and Marine Le Pen in France, as well as the growth of pro-EU civil society groups such as the German-founded Pulse of Europe and the tactical-voting group Best for Britain.