Thanks everyone for your input! It's greatly appreciated. I've often wondered what people do when they win Bitcoins from a foreign online casino, for example, and whether they owed taxes to the country where those Bitcoins originated, in this case the foreign-owned casino.
That depends on where you live. In the UK there are no taxes on gambling winnings at all.
If you live somewhere where you are taxed, you'd pay taxes to the country you live in. It's your windfall therefore your nice problem to have.