In 2045, Climate change might result in border locking, both on a national and on EU level. With increased mobility of climate refugees, we might be facing a refugee crisis similar to or most likely bigger than that of 2015. 

Recent years have shown a rise of right-wing attitudes and popularism both in the UK but also in many EU countries. With Brexit, the UK now has the option to decide on its own whether it wants to close its borders to refugees and migrants or keep them open for them. They could be more flexible in handling migration than the EU because they are independent. On the other hand, they also have to face any arising challenges on their own. 

At the same time, the EU could go into border locking. As we have seen in recent years, the securitization of borders now happens along EU lines, instead of nationstate lines. Or it could open borders up again. Depending on the EU developments, the UK could become a major destination for migrants and refugees (or not).