alt Hacker NewsThis isn’t an accurate interpretation. The UK is a _constitutional_ monarchy, not an absolute monarchy, meaning that the monarchy exists and acts in accordance with the constitution.
In the case of the UK, some of the rituals (such as the one you’re referring to with the prime minister) are based on longstanding traditions, because humans are weird and we like those sorts of things, but the requirement to do that stems from the constitution, not from the King deciding if he likes the PM or not.
And to be clear, the UK constitution is really the combined law passed over centuries (including the Magna Carts). There is no single, “sacred” document as in the US (which isn’t really sacred in practice - we can amend it or let SCOTUS re-interpret it).