It was the last event of the meet anyway, so they were never likely to do a swim off. If they wanted to decide in advance based on a race, more likely on a meet like Mare Nostrum.
Both are pre-selected anyway because of the relay, so they both will be there anyway. Whichever gets the nod, we probably won't know until the week of.
With GB's history of messing about, especially in the first year of a new Olympic cycle, who knows what we'll do. Knowing us, stick Tom Dean in there, make Duncan do the 200 fly and Jimmy the 400 free.