The customer services team at British Airways is often the face of the company to customers. In this role, you will be expected to know all of the details on flight scheduling, ticketing, baggage policies, and many other areas of the business, so you can explain details to customers in your interactions with them. To get at your ability to be as knowledgeable as possible in this role, your interviewer is asking this question to see if you've had to do this in any previous roles you've held. As you answer this question, talk about the position you've held that required a vast knowledge base about the organization you worked for, and explain why having that knowledge was critical to the role. Make sure that you also reiterate to your interviewer that you are willing to learn and master every aspect necessary for this role.