Yes, British Airways generally allows you to take a wedding dress as part of your hand luggage, but it counts as your one piece of cabin baggage. BA's standard cabin bag size is 56cm x 45cm x 25cm, which can be quite small for a voluminous ballgown. If your dress is in a slim garment bag, many BA crew members—known for their "above and beyond" service for special occasions—will allow you to hang it in the onboard wardrobe at the front of the plane (usually reserved for First and Business class), though this is strictly on a "space-available" basis and cannot be guaranteed in advance. If the flight is completely full, you may be asked to lay the garment bag flat across the top of the suitcases in the overhead bins. To protect the dress, many brides use a specialized "acid-free" wedding dress travel box that fits the BA size requirements; these are designed to prevent creasing and allow you to keep the dress with you throughout the journey. It is always a good idea to arrive at the gate early and politely mention to the gate agent and the lead flight attendant that you are traveling with your wedding dress to increase your chances of getting a little extra help.