Thomas Cook is close to bankruptcy. They don't have enough money to keep their airline going through the winter. They've asked the banks for money. Lots of volatility in the price. Brexit is likely to just make things a little riskier and a little trickier for them because people are confused about what happens before and after Brexit even though their passport expiry dates are well in to the future. Dumbasses! You think that your passport just expires when Brexit happens? Dumbasses!