The EU could "implode" if British voters opt to go it alone in June's referendum, warns European Parliament President Martin Schulz.
In a newspaper interview, the German deputy spoke of an "implosion of the EU" if the UK were to leave the EU after the June 23 referendum.
He told German newspaper Frankfurter Allgemeine Zeitung that other member states will want "escape referendums" if Britain opts out.
The Socialist MEP cautioned against "enemy movements within Europe" and the rise of left or right wing populists which may come to power. Citizens have lost trust in national and European institutions and fundamental reforms are needed to make the EU more effective.
"The EU has been on a sliding slope for some time now," Schulz said. He added that extremists are still a minority, but last week's Dutch rejection of the association agreement with Ukraine shows that "we should not rely a good ending" for Europe.
He told the paper, published on Tuesday, that, "the EU was created as a tool for solving problems, but many people think of it as a part of the problem rather than a solution."
His fears of an "implosion" are partly echoed by Giles Merritt, founder and Secretary General of Friends of Europe, who told this website, "Martin Schulz is quite right that if the British vote for Brexit they'll be triggering a Europe-wide political storm.
"What is much less certain is the sort of chaos that would ensue. His warning of an 'implosion' is credible, but it seems equally possible that the UK's exit could mark an upturn in the EU's fortunes.
"The shock of a Brexit might end the shilly-shallying over meaningful EU reform. Berlin and Paris could make themselves the hard core of a political union that would re-launch the European project."
In another intervention in the Brexit debate, Jo Leinen, another leading German MEP, called Britain "a little island in the Atlantic" and said Brexit would leave it weaker.
"This is the 21st century. Britain is no longer an empire."
He said, "The UK will lose influence on the continent and worldwide if it quits the EU."
He insisted that the EU should look to integrate more rather than disconnect.
Meanwhile, claims by Parliament Vice-President Alexander Graf Lambsdorff that MEPs are unlikely to endorse David Cameron's renegotiation deal if Britain chooses to remain have sparked further angry comment.
Sajjad Karim, an ECR MEP, said, "The deal was agreed by all our national leaders, including Angela Merkel. While a few MEPs from some smaller delegations and groups may have their reservations, ultimately the Parliament will back the national leaders."
Further reaction to Lambsdorff's remarks comes from Jayne Adye, campaign director of leading cross-party, grassroots Eurosceptic group Get Britain Out, who told this website, "Ever since the Prime Minister returned from Brussels, he has been claiming victory over his 'deal' to reform the EU. The phrases 'special status' and 'fundamental reform' have been repeated time and time again.
"Cameron's so-called renegotiation 'deal' was pathetic for many reasons, one of the main reasons being, it is not legally binding. It would merely require the Court of Justice to take his negotiation deal 'into account'."
She added, "Even if it was legally binding - which it isn't - the entire process was irrelevant, as he asked for so little and achieved even less.
"Now we hear, the only parts of the renegotiation which could be implemented - if the European Parliament agree - may be rejected as well. This won't make a blind bit of difference, as the great British public saw through David Cameron's lies a long time ago.
"The EU referendum won't be won or lost on this PR stunt; it will be decided on whether Brits want to be a sovereign democracy once again, and we want to get Britain out as soon as possible."
Elsewhere, former UK foreign secretary David Milliband has said that leaving the EU would be an act of political arson that risks the destruction of international order.
In one of the starkest warnings of the referendum debate so far, Miliband argued that the impact of Brexit could extend far beyond the UK and that it could have a disastrous effect on the rest of the world.
He said it would amount to "giving up on our alliances" with the rest of the world.