> There’s no need to speculate, the reason we say Parliament is sovereign is that Parliament ordered Charles I executed for defying them.

Quite arguably, you can’t, but monopoly power (particularly, its expression as pricing power) can be observable (and itself proves an actual monopoly) when monopoly would not be clear by other means.

The ability to price without sales going to a competitor demonstrates the absence of actual competition, regardless of the superficial apparent competition in a described market.