John Bercow has shown he will play a pivotal role in the Brexit endgame – here's how

John Bercow, the speaker of the House of Commons, has been accused by ministers and Conservative MPs of showing anti-Tory and anti-Brexit bias after he allowed a controversial vote to go ahead.

His critics claimed he ripped up centuries of tradition by calling a vote on an amendment to a government “business motion” setting out the timetable for the five-day debate on Theresa May’s Brexit deal. Unusually, he overruled the officials who advise him, the Commons clerks. Eurosceptic MP Peter Bone claimed they had previously told him the technical motion could not be amended.

Dominic Grieve, the former attorney general, tabled an amendment saying that if May’s deal is rejected by MPs next Tuesday, she must table a motion on the government’s Plan B within three sitting days – by 21 January. Previously, she would have had three weeks. Grieve’s proposal was approved by 308 votes to 297, the government’s second defeat in 24 hours.

Does it matter? In any case, May would have had to respond quickly to a defeat on her deal; leaving a vacuum would have left her premiership looking even weaker. In a break with the tradition of not criticising the speaker, May said she was “surprised” by his ruling and that there should be “consistent interpretation” of the Commons rulebook. She plans only a 90-minute debate if her deal is voted down. But ministers fear Bercow will cause them further headaches; procedural wrangles are inevitable, so he will play a pivotal role in the Brexit endgame. He will not be cowed by this week’s criticism.

The Grieve amendment will limit the amount of time May will have to wring more concessions out of the EU. Her original breathing space would have heaped more pressure on MPs worried about a no-deal Brexit to back her, by taking the UK closer to its 29 March departure. The amendment will probably allow MPs to vote on alternatives to May’s agreement earlier in the process.

Did Bercow break the rules? No. The speaker is the final arbiter on interpreting the rulebook. Characteristically, he portrayed his decision as safeguarding the rights of backbenchers.

Critics believe his move will have long-term implications. It could allow backbenchers to pass similar amendments in future, loosening the government’s grip on the Commons timetable, a precious asset. However, whether Wednesday’s ruling is a one-off or sets a precedent will probably be decided by Bercow’s successor.

The row is the latest in a series of clashes between the speaker and the government. He has allowed parliament to hold ministers to account by forcing them to answer many more urgent questions on topical issues than under his predecessors, which means they are summoned to the Commons at short notice. The number rose from 12 in his first year as speaker to an average of 50 since.

It is difficult for ministers or MPs to remove a speaker, although Michael Martin stood down in 2009 after criticism of his handling of the MPs’ expenses scandal.

When Bercow succeeded him, he said he would serve for nine years, a term that ended last summer. He carried on, resisting moves by some Tories for him to quit over the bullying and sexual harassment of parliamentary staff by MPs. Bercow strongly denied allegations that he had bullied officials. Although he was a Tory MP before becoming speaker, Labour was keen to keep him in place for the Brexit process because of his fierce independence. Tories point to his admission to a group of students that he backed Remain in the 2016 referendum. He will come under further pressure to stand down this summer – if Brexit has been resolved by then.