The UK Film Distributor's Association website has announced a Friday April 29th 2016 release for the upcoming "Batman vs. Superman" film, releasing it one week ahead of the United States of May 6th.
The early release overseas is no huge surprise. The April/May window has proven a boom time to open Hollywood blockbusters earlier overseas. It's going on right now with "The Amazing Spider-Man 2" opening this week in several global markets to take advantage of both the Easter Holiday and school holidays currently happening in various countries. There's also extra pressure this year to go early before the World Cup shrinks the global filmgoing audience for a few weeks.
There's no word on Marvel's plans for the UK for "Captain America 3" and whether it will go a week or two earlier as well, but Marvel's "Iron Man" was the film that really began this trend and the studio has released all its 'start of Summer' superhero films at least one week earlier overseas over the past few years.