If British voters choose to leave the European Union on 23 June it could be the beginning of the end for the bloc and for western political civilisation, Council President Donald Tusk said.
A spokesperson said Commission President Jean-Claude Juncker thought the same.
In an interview with German newspaper Bild, Tusk said a vote for Brexit would provide a major boost to radical anti-European forces who he said would be “drinking champagne”.
“Why is it so dangerous? Because no one can foresee what the long-term consequences would be,” Tusk said. “As a historian I fear that Brexit could be the beginning of the destruction of not only the EU but also of western political civilisation in its entirety.”
Everyone in the European Union would lose out economically if Britain left, Tusk said.
“Every family knows that a divorce is traumatic for everyone. Everyone in the EU, but especially the Brits themselves, would lose out economically,” he said.
Asked to comment if the Commission shares the same fear, spokesperson Mina Andreeva said that Tusk and Commission President Jean-Claude Juncker were meeting often and thinking alike.
“President Juncker and President Tusk meet regularly. They will have a working lunch tomorrow (14 June) for example. They discussed the matter [Brexit] several times and therefore President Juncker has conveyed exactly the same message in his own words, for example on 12 May in Berlin”, she said.
On 12 May Juncker participated at the 19th International West Deutscher Rundfunk Europaforum “Europe without Europeans?”., where he called the possible Brexit scenario a “catastrophe”.
“Brexit would be a catastrophe. […] If Great Britain decides to leave the European Union, it will create a multitude of problems that the British people do not see because they have not been well informed”, he said, adding “If Brexit unpicks the EU’s jumper, we have to knit a new jumper”.
Juncker also regretted that the summit deal clinched during the night of 18-19 March between the UK Prime Minister and the other 27 EU leaders to help Cameron campaign for the Remain camp had been completely absent in the pre-referendum debate.
“Nobody is talking about the agreement struck between Cameron and the other 27 national leaders on 18 March, that plays absolutely no role in the debate. We spent weeks working with the Brits to the find possible solutions to their demands, but this deal is nowhere to be seen in the British newspapers or television”, Juncker said.
The latest polls show British people are almost evenly split over whether to stay or go.
Although he expressed hope that the EU would survive in the event of a Brexit, Tusk said the price would be high.