Not if ground rental at Zeebrugge is cheaper than the current UK locations. Asked around at work and a lot of these are coming from inland depots as well as some stored on Port premises, checked manifest yesterday and Rick is correct, vessel arrived empty.
Majestic Maersk loaded over 2500 and so far Maersk Bentonville, has or will, move with these recent voyages another 3500 (figures approximate), that's a lot of empties and represents a lot of rental for storage.
The Maersk agent I spoke to on Majestic Maersks departure on the quay said the Triple E was the cheapest way to get these boxes back to the far east, there's currently plenty of space on board so might as well fill it with empties, additionally Majestic Maersk was steaming back at super slow speed to maximise efficiency.
If you have to move a lot of cargo as cheap as possible then the Triple E is their best vessel, however, no idea if Triple E's current berth at Zeebrugge.