Prerogative powers was formerly exercised by the monarch acting on his or her own initiative . Since the 19th century , by convention , the advice of the prime minister or the cabinet — who are then accountable to Parliament for the decision — have been required in order for the prerogative to be exercised . The monarch remain constitutionally empowered to exercise the royal prerogative against the advice of the prime minister or the cabinet , but in practice would only do so in emergencies or where existing precedent do not adequately apply to the circumstances in question .