Polish president Andrzej Duda has warned that the European Union could face collapse if Britain decides to leave the bloc following a referendum that could come as early as this summer.

The 28-nation EU is negotiating a reform of EU rules aimed at discouraging a British exit by cutting red tape and restoring some decision-making back to national capitals.

If British Prime Minister David Cameron gets the reforms he wants, he feels that a referendum could decide Britain should remain a member. With its free-market orientation, robust foreign policy and nuclear capabilities, Britain has been an important if often-reluctant member. Duda said a departure would be devastating.

Duda said he thought "it would lead to a big crisis and even a collapse if the U.K. left."