Since the 1800s, the sovereign of the United Kingdom has, in practice and then in constitutional theory, required to carry out the "advice" of the government. "Advice" here does not have its vernacular meaning -- it's not the government saying "we think this would the best course of action, would you mind terribly signing at the top please?", but (to adapt the saying minted for the "election" of a bishop in the Church of England) "advice" like shoving the monarch out of a third-story window and "advising" her to fall. (She is entitled to be informed of all major government programs, so she receives major briefing papers. She had a weekly audience with the prime minister, and it has been suggested that she tries to influence the government then. But we don't know for certain.)

She is required to sign all laws put before her, writing "the Queen wants it" (in a variety of French). Very nearly every proclamation is written by the government and issued starting with "BY THE QUEEN A PROCLAMATION". She is not allowed to give any substantive public remarks other than what the government commands. It would nowadays be seen as outrageous were she to refuse to carry out the government's will.