I do not think Bitcoin is a threat to both. Because basically everyone who holds Bitcoin will still exchange their Bitcoin with local currency, in order to be used to transact traditionally. We know that Bitcoin can only be used online, while dollars and poundstreling can be used online and offline for wider transactions. So, Bitcoin is not a threat.
Exactly. I agree wih you. Without fiat i dont know how can we be able to determine the value of our bitcoin, through sacks of grain, bars of gold or what? They are two separate currencies with different uses. Like gold, you will never know the value of it per gram without fiat or local currency unless you trade them for commodities with no exact and specific amount or value per transaction.