From a legal perspective, it gets much simpler if it's <0.5%, so if you wanted to do it by the book then it gets much easier if you sent wort with newly-pitched yeast - but obviously that gets unpredictable from a bottle bomb point of view! Maybe less so at this time of year.
But broadly, at the UK end I don't think anyone will get too worried about the odd bottle of beer, if no money is changing hands. It gets very complicated if it's happening commercially though. Label them as "water samples for analysis"? Brown, with visible sediment, in a plastic bottle? Noone's going to look too closely...
You might want to think about transport though - an aircraft hold is cold and low pressure.