What is the Grieve amendment and why is it important to Brexit?
By Joe Harker
An amendment put forward by Conservative MP Dominic Grieve and passed by the House of Commons has been hailed as a "game changer" on Brexit.
The vote was 308 to 297 in favour of Grieve's amendment and it means that if the prime minister loses the meaningful vote on her deal, scheduled for January 15 and expected to result in a heavy loss for Theresa May's deal, she must set out her plan B within three sitting days of parliament. It is yet another blow to the power of the prime minister as she will be forced to work to parliament's timetable in the likely event of her deal being defeated.
Had the amendment not gone ahead May would have had 21 days to make a statement on the government's next course of action, which would then have required a vote in the Commons within the next seven sitting days of parliament. The much tighter timetable forces the prime minister to have her alternative plan ready if her deal is voted down, she can't play for time as she has done for so many months.
The successful vote on the amendment was granted by speaker of the house John Bercow, who has been criticised for going against the will of Downing Street by choosing the amendment for a vote. Downing Street officials said the Grieve amendment would be debated as a matter of procedure but not voted on so Bercow's decision to put the matter to the Commons was seen as a defiance of the prime minister.
BBC parliamentary correspondent Mark D'Arcy explains that Bercow's decision to put the Grieve amendment to the Commons "drove a coach and horses through accepted normal practice" and sets a new precedent for the way parliament operates.
Writing in The Guardian, Anne Perkins argues that Bercow's decision to bring the amendment to a Commons vote "endangers the office of Speaker, and our democracy".
The government believed their motion setting out the timetable for Brexit debates was unamendable, with no room for changes or meddling from MPs. Government ministers who drew it up considered the motion to be "bomb proof".
Commons leader Andrea Leadsom wrote that "no motion to vary or supplement" the government's motion could be made "except by a minister". Bercow argued that such rules did not rule out an amendment to the original motion. A motion is a proposal put forward for debate or decision by the Commons, an amendment is a proposed change to the wording of a bill or motion. In such small differences are the massive changes to the Brexit timetable made.
The Grieve amendment has imposed a strict timetable on the prime minister if her deal fails to be approved during its scheduled vote in the Commons. Having run the clock down on Brexit to increase the threat of a no deal exit and scare MPs into voting for her deal this is a crushing defeat for Theresa May. If she loses she will no longer be able to set the timetable for proceedings.