It has been clear for some time now that John Bercow sees himself as a leading protagonist in our political drama, not some bystander. Even before Theresa May’s deal was bogged down in parliamentary trench warfare, the Commons Speaker had styled himself as a warrior on behalf of the legislature, defending it against arrogant incursions by government. But kicking May’s withdrawal agreement out of the chamber altogether yesterday was a ferocious escalation.

The premise is procedural and venerable. Erskine May, the vast tome in which are accumulated the various rules and conventions governing parliamentary business, decrees that the same motion cannot be debated twice in one parliamentary session. And since May’s Brexit deal was rejected last week, Bercow believes that the prime minister cannot simply come back – as had been planned – and ask MPs to reconsider. What was billed as a third “meaningful vote” would need some substantial revision of content to qualify as truly meaningful in the Speaker’s eyes.

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Views on whether or not Bercow has gone rogue will tend to follow previously held opinions on a man about whom few MPs have neutral feelings. He has been mired in a running vendetta with the right wing of the Tory party, which failed in a coup attempt to unseat him in 2015. But Bercow also knows that history is being made on his watch. He could have been discreet, subtle, unassuming – the defuser of rows and the lubricator of compromise. Or he could get stuck into the fight. He could be remembered by historians in a series of easily skipped footnotes or he could end up having a chapter to himself. It is clear from yesterday’s action which option he prefers. Bercow knows his Speakership will not survive much beyond Brexit anyway. His enemies will come for him again, and he doesn’t have all that many friends.

That doesn’t mean his decision is capricious or unconstitutional. The relevant procedural scriptures seem pretty clear on the matter, so the Speaker is well within his rights to interpret them as he has done. But it is still a matter of interpretation, and so unavoidably a heavily political action. It blasts the prime minister’s plans for the week off course. It transforms the calculations that MPs make about what should happen next. It also retrospectively casts a darker, more terminal shadow over the decision a majority of them made to reject the deal last Tuesday. Might some Tories or members of the DUP have acted differently had they known it was May’s last shot at getting her deal through?

Certainly the prime minister’s strategy has depended on eliminating options, so that eventually MPs would conclude that the only feasible Brexit on the table was hers. For that to work, she needed to keep bluffing and keep raising the stakes. She didn’t realise that ultimately, in parliament, it’s the Speaker who runs the game. And now all bets are off.