LONDON — Britain has never had a proper, written constitution, a matter of some pride to Britons. While Americans haggle over their rules, British politics runs on an evolving array of laws and practices, refereed by the so-called good chaps in government, with their impeccable sense of fair play.

But popular faith in that approach was severely shaken this past week when Prime Minister Boris Johnson decided unilaterally to suspend Parliament at the height of a political crisis set off by his determination to achieve Brexit by an Oct. 31 deadline, with or without a deal with the European Union.

And that first shock was followed by a second, perhaps even more startling realization: Once someone starts kicking aside the conventions and customs that shape British democracy, there are surprisingly few hard and fast checks on executive authority.

[Throngs took to he streets to protest Boris Johnson’s move.]

Despite the howls of outrage from Mr. Johnson’s opponents, historians and legal experts say Britain’s entire political class has to shoulder the blame, having taken a series of steps in recent decades that opened the door to these sorts of disruptive tactics.