LONDON — Along with the angry braying and ornate insults that were the soundtrack to Brexit debates this past year in the British Parliament, there was, for better or worse, a certain kind of choreography that kept proceedings on track.

Government ministers gave way to questions from the opposition. The speaker shouted, “Order!” and lawmakers, for a little while at least, lowered their grumbles. Both sides kept showing up.

But that sense of consensus, however stylized or superficial, was blown apart around 2 a.m. on Tuesday. In remarkable scenes that flustered even the sotto voce BBC commentators, opposition lawmakers threw themselves at the silk-canopied speaker’s chair, trying in vain to keep him from getting to his feet and allowing Parliament to be suspended.

When a security team finally tore the lawmakers away, the speaker, John Bercow, remained studiously seated, causing one of the BBC commentators to marvel under her voice, “He’s not going to go.”