All sorted.
Via the hotel (Alvear Icon) we have now organised for antigen tests to be carried out in our hotel room. The hotel was very helpful with this, and it is the easy option.
I have half-a-memory of reading somewhere that short cruises didn't need pre-embarkation testing whilst longer cruises did. It didn't make sense at the time, but people on the 10 day cruises saying they don't need a test seems to make it the case. Anyone understand the logic of it?