If you want go to third level where you can go shop at the Duty free near security checkpoint. If you need purchasable the Duty Free before you headed to security checkpoint. They will be delivered right at your boarding door. If you need purchase inside security where you walked to N4 in the concourse B near British Airways lounge. You need to do filled the customs forms before you are landed into your final destination cities. I'm sure if you have anything more questionable for your concerns.