[LeonB]

If the King — without the support of the general populace or of the parliament, but acting in his own interests, like a king of old — dissolved the Parliament, he could and very swiftly would be ousted, legally.

The line of succession would be followed until an individual was found who was willing to support the democracy. This was proven in 1685.

They swear allegiance to the King (or Queen) — but it’s understood that a new King or Queen can be swapped in. The extremely stilted and socially restrained manner in which Queen Elizabeth (for example) behaves is because they entirely know that their family does not hold the nation hostage, it’s quite the opposite.