Dramatic scenes in the Commons on Wednesday saw MPs challenge the Speaker in angry points of order for more than an hour, and the House divide into almost equal factions.
For John Bercow’s critics on the government benches, he had undermined the authority of his office and established a dangerous precedent by allowing MPs to amend a motion hitherto regarded as unamendable.
To his admirers, who included Conservatives as well as opposition MPs, he was a fearless champion of the right of parliament to assert itself against the executive.
Leaving the argument over procedure aside, however, the House's approval of Dominic Grieve's amendment to the motion on Theresa May's Brexit deal could prove to be a hinge moment in the story of Britain's withdrawal from the European Union.
It represents parliament’s long-anticipated move to take control of a process that the minority Conservative government has shown itself incapable of managing successfully.
If the prime minister’s deal is rejected, as expected, next Tuesday, she will have just three sitting days to come back to parliament with a motion outlining what she proposes to do next.
That motion will be amendable, allowing MPs to test support for alternatives, including a Norway-plus model that would see Britain remaining in the single market and the customs union, and a second referendum that could stop Brexit.
MPs demonstrated in a vote on Tuesday night that a majority opposes leaving the EU without a deal. But if the prime minister is unable to pass her deal, what chance do the alternatives have of winning a majority?
Before the Christmas recess, support for Norway-plus appeared to be seeping away as Remainers, particularly on the Labour benches, started to believe that a second referendum was achievable. Labour seemed poised to take the steps agreed at its party conference last year that would lead it to support a second referendum, favoured by most of its members.
Since parliament returned this week, however, the Labour leadership’s lack of enthusiasm for a second vote has remained undiminished and some wavering MPs have become anxious about the potential toxicity of another referendum.
In the chamber yesterday, Conservatives Oliver Letwin and Ken Clarke were negotiating in public with shadow Brexit secretary, Keir Starmer, about the kind of compromise Labour could accept.
A cross-party majority has revealed itself at Westminster this week to oppose a no-deal Brexit and assert parliamentary control over the withdrawal process. But it has yet to marshal itself behind a single plan for Brexit, without which Britain will crash out of the EU on March 29th.