Probably knew someone who worked on the set, got it from the script writers/actors, etc. Maybe the €264 equated to the maximum amount Ladbrokes would take. I sent Mrs. Catcher to have a novelty type bet with them a while back (on foot of a tip from the erm) and they accepted a precise (not round figure) max stake. If he went to Ladbrokes first and, not being a punter, assumed they would take whatever he wanted to bet so put a grand on the counter of which they took €264 it'd explain approaching other firms with the same amount based on the assumption that they all work the same way.