I too have the BA branded Chase Visa - and am aware of the 3% foreign transaction fee - I tend to avoid using the card abroad but did so on a recent trip.
I had a foreign charge billed in USD - and no 3% was added. I had foreign charges in another currency - and the 3% was added.
Was the transaction that you've been charged the fee for, a US Dollar transaction? If not, which currency was it in? Where is your itinerary originating?