I think Bitcoin is not a threat to both because Bitcoin is just digital gold.
Bitcoin has value when it comes to PAIR with FIAT like USD and Pound Sterling.
If Bitcoin is Paired with Altcoins, then there is still no value.
Indeed, Dollar and Poundsterling should not worry bitcoin will take over. Many country in the world still dont know about bitcoin but if bitcoin become acceptable in many country, bitcoin can take dollar and poundsterling place because bitcoin more safe to carry and more secure