According to John Bercow he has chosen to step down on 31 October because it would be the ‘least disruptive and most democratic course of action’ if he stayed on for the votes on the Queen’s speech expected in the last week of October. But there is a somewhat glaring reason for choosing the last day of October – it is a none-too-subtle hint that he sees it as his duty to frustrate Britain’s departure from the EU, which was due on that date but which, thanks to the law passed by Parliament today, now seems likely to be delayed again. Going for that date is Bercow’s way of saying ‘job done’.

Two years ago, following the 2017 general election, Bercow went back on his previous intention to step down some time in 2018. He had changed his mind, he said, and intended to serve for the entire Parliament, due to end in 2022. Why extend his tenure in the Speaker’s chair then curtail it? The extra time meant that it was Bercow, rather than a new Speaker, who chaired debates on a Brexit deal. And what a role he has played. The Speaker’s impartiality has gone out of the window as Bercow has given rebels an advantage, sometimes quoting precedent and sometimes discarding it.

It was thanks to Bercow that the Commons was able to seize the business of the Commons a fortnight ago under Standing Order 24 – a process by which backbenchers can demand an emergency debate. It is in the Speaker’s discretion whether to allow such a debate – and applications are rarely successful. Bercow has chosen to announce his departure on the very day that the resulting law completes its passage through Parliament.

In January this year Bercow allowed Dominic Grieve to table an amendment to a government procedural motion – a type of motion, as Theresa May protested, which is not normally amendable. Commons clerks had advised the Speaker on that point. Bercow, however, decided that he would innovate. ‘I am not in the business of invoking precedent, nor am I under any obligation to do so,’ he said. ‘If we were guided only by precedent, nothing would ever change.’ The amendment – requiring the government to come to the Commons within three days and explain how it intended to proceed – was duly passed by the Commons.

Yet two months later, when it suited him, Bercow turned into a great stickler for precedent. Theresa May was keen to bring a third vote on her Brexit deal before the Commons, having suffered heavy defeats in her first two attempts. Bercow ruled that the Commons could not be allowed to vote on it, because it was a motion substantially unchanged since the last attempt. He justified this by quoting a convention dating back to 1604 and which, he said, had been used a dozen times since, though not since 1920.

There is only one explanation for these two opposing attitudes towards observance of precedent – by realising that in both cases Bercow was acting clearly in the interests of those who are trying to thwart Brexit. His bias has shown up several times, too, in his choice of which amendments to select for debate. In March, for example, he selected two motions which would have allowed MPs to seize control of the business of the House of Commons away from the government (in the event both of which were rejected by narrow margins). He blocked, on the other hand, a motion which would have allowed MPs to rule out a second referendum on Brexit. In January, when Theresa May was on her first attempt to pass her EU withdrawal bill, Bercow similarly rejected an amendment which would have put a time limit on the Irish backstop.

John Bercow has often posed as the backbenchers’ friend during his time as Speaker. But in recent months he has played a far clearer role – as the friend of Remain.