Q:

What is the difference between 退欧 and 脱欧? 

On RFI Chinese Radio, they often have a topic about what I got to understand is Brexit, a current issue in England.  They often use at different time the terms 退欧 and 脱欧 to talk about the issue.  From what I understand, it's about separation of England from the European Union, but I can't get hold of the difference between these two expressions.  Does anyone have an idea ? 
Edit
First, thanks to @水巷孑蠻 for the answer which seems accurate.  I accepted that answer but now @Tang Ho's answer bothers me. 
What I find is that 退欧 and 脱欧 could be interchangeable.  But now, it is implied that it could be depending on how the organization of England vs Europe is viewed by narrator.  Both answers seem valid.  How to choose ?  

A:

Those two terms can be interpreted in this way. 
退歐 refers to the intention of exiting (hence ‘Brexit’) or withdrawing from EU.  This process involves a referendum and is now completed. 
脫歐 would involve some physical action of breaking away from or severing connections with EU.  This process has not yet started. 
But people are, no doubt, using those two terms interchangeably.