Just to welcome you to Flyertalk Sara Louise Hodgson and to welcome you also to the British Airways forum. As the name suggests, we're probably not the best equipped to help. Thinking aloud, I would guess that Thomas Cook would have the information somewhere but typically the easy access databases get wiped down after holding recent data for a few months. I imagine that data protection laws would give you some potential avenue to get this information, and you could thereby liaise with the data controller, but the formal process is deliberately a bit cumbersome. It may be a case where if that is the only information you need, a quick call to the data controller office may get you unofficially what you want, but that is speculation on my part.