Only fleets in a sea zone can attempt to intercept enemy fleets passing through that zone. Fleets in ports have no say in the matter at all.
However, the move is illegal because it is farther than the Reserve can convoy an army (14.23).
Thanks. I had a cantankerous player.
It's actually not too far. I was mistaken. It was actually Copenhagen to Bordeaux. That's 5cp length, equal to the Swedish Reserve card.