Sorry for my ignorance but I've not done BA to Barbados before. So you just go and check in at IAM then get wined and dined ? Then they get you to the plane in time for pre flight drinks presumably (hopefully)?
Your car will drop you outside the IAM center. you check in as if it was the main airport ,then upstairs to the lounge very small only about 20 seats and no hot food, when it is time for departure you are taken to the main airport by car or minibus.