I think intent matters here. If I exchange currencies because I intend to buy goods & services with it, then it's no different than stopping by a Thomas Cook/T

I think intent matters here. If I exchange currencies because I intend to buy goods & services with it, then it's no different than stopping by a Thomas Cook/Travelex. However, if I'm trading in & out of Bitcoin because I'm arbitraging it, then I'm a trader, not a traveler. And should pay tax on the profits.