In the UK, in practice, the government has power, but in theory the power lies in the hands of the Monarch, who acts on the advice of her Ministers.
The Prime Minister advised the Queen to prorogue Parliament, and she duly did so. The Supreme Court has since found that that advice was unlawful. Therefore, they say, Parliament has not been prorogued.
“This court has already concluded that the prime minister’s advice to Her Majesty was unlawful, void and of no effect. This means that the order in council to which it led was also unlawful, void and of no effect and should be quashed. This means that when the royal commissioners walked into the House of Lords it was as if they walked in with a blank sheet of paper. The prorogation was also void and of no effect. Parliament has not been prorogued. This is the unanimous judgment of all 11 Justices.”
How, though, does this jibe with the legal fiction that Her Majesty has the power to prorogue Parliament whenever she so wishes, and that the Prime Minister merely advised her to do so, having no power to order her? If his advice was unlawful, surely her action in response to that advice was nonetheless lawful, as the fiction is that she acts in her own right, not merely as an automaton controlled by her Prime Minister.