The primary driver behind Bitcoin's value is a growing realisation, triggered by the 2008 financial crisis, that fiat currencies are vulnerable in a way that Bitcoin is not.
1. Bitcoin is not controlled by any government requiring re-election
2. Bitcoin is finite
Every fiat currency in the world is now pegged to one of the 5 reserve currencies (US dollar, Euro, Yen, Swiss Franc, Sterling).
When the next financial crisis hits, where do these currencies go?
Interest rates are already < 1%. Quantitive Easing has been all but exhausted. So what's left?
The only way to keep the rabble off the streets will be to starting sprinkling €500 notes from ECB helicopters.
When that happens, Bitcoin takes over.
Note: CGT is due on Bitcoin gains even if you never convert back to fiat. If you bought BTC at €100, and its now worth €1,000, and you use it to buy something, a CGT liability arises.