Central banks or any other bank does not have any kind of control on it and i think they cannot affect the bitcoin prices directly. But yes they can be a headache to the Cryptocurrency users by modifying the Exchange rates, terms & conditions while exchanging the Bitcoin and other crypto coins with the Fiat currency, which can lead in creating some impact on the bitcoin prices for sure. And yes there is no speech that can affect the bitcoin prices like BOE, Federal Reserve, but we can create the panic selling or buying by spreading the Rumours and doubts in the mind of the traders.