Sorry if this has been discussed elsewhere; didn't see it anywhere. If it has - Kham or someone can just delete this.
This is just a theory on my part - nothing confirmed & haven't read it anywhere.For those of you that don't watch "Rebels Recon" from all the Episodes of Star Wars Rebels - let me catch you up to speed on something.
Every episode, from the very start, has featured a jokey live-action segment with a Chopper replica doing stuff around the LucasFilm offices, acting just like he does on the show.
In the last episode of Season 2, they crypically packed him in a box and slapped a Union Jack sticker on it.
The first episode of Season 3 made a big deal of Chopper's return to the LucasFilm offices after his time away in the UK and every episode this season has in some way played up the fact that Chopper was in the UK without offering any explanation whatsoever why he was there.
What's this got to do with Rogue One?
Like other Star Wars movies - a lot of it was shot at Pinewood Studios in the UK.
http://www.imdb.com/title/tt3748528/locations?ref_=tt_ql_dt_6Maybe I'm reading too much into it - but for the life of me I can't think of any other possible reason why they would be cryptically playing up the fact that "Chopper" spent a lot of time in the UK, again, with no explanation of any kind at all. Just constant reminders that he was in the UK.