Amid scores of Brexit amendments and chaos in parliament, there are only two votes that really matter – here’s why

Tuesday will be a big day in the Brexit story. We have had historic votes and critical moments before, but this is up another notch. The vote on the amendment jointly proposed by Yvette Cooper, Labour MP, and Nick Boles, Conservative MP, will be both historic and critical.

It will be historic because it is the first time since the 17th century that the House of Commons has tried to take control of the nation’s affairs from the government. And it will be critical because no one knows which way the vote will go.

The Cooper-Boles plan is to take no-deal Brexit “off the table” by requiring Theresa May to seek to postpone our departure from the EU if a deal has not been approved in time.

The vote will be no mere expression of opinion. If the amendment is passed, it will change the rules of the Commons to allow a bill drafted by Cooper and Boles to be rushed into law on 5 February.

There is some talk of this bill being blocked by Eurosceptic peers in the House of Lords, which would have to whizz it through on the same day. Unlike the Commons, the Lords doesn’t have rules for timetabling debates, which means a small group of peers could keep talking to prevent votes. But Labour and Liberal Democrat peers insist that the huge majority opposed to a no-deal Brexit in the House of Lords would invent new rules, if needed, to get the bill through.

So the big question is whether the amendment has the votes it needs to win in the Commons on Tuesday night. Last week I wrote that I thought it had. Since then I have been through the numbers in more detail and it could be tight. I have assumed that 24 Tory MPs who are strongly opposed to a no-deal Brexit would break the government whip to vote for Cooper-Boles; and that 15 Labour MPs who are opposed to delaying Brexit would break their party’s whip to vote against it. It would then pass by just three votes.

Boles himself says “it will be nail-bitingly close”. I think he is being cautious. If Labour doubters such as Lisa Nandy, MP for Wigan, abstain rather than vote against, that will help him; and I think there are many more than 24 Tory MPs who are worried about leaving the EU without a deal.

After all, much of the cabinet is poised to resign to prevent that happening; Amber Rudd wanted ministers to be given a free vote on Tuesday; and Philip Hammond says a no-deal Brexit would be a “betrayal”. As ministers they will have to vote against the amendment, but their comments will encourage soft-Brexit backbench Tories to rebel.

The Cooper-Boles amendment will not be the only drama on Tuesday night. There are already 14 amendments on the order paper, and more could be tabled on Monday. We don’t know how many speaker John Bercow will select, or how many will be pushed to a vote, but another important vote is likely on one of the amendments backed by Graham Brady, chair of the 1922 Committee of Tory backbenchers.

Most attention is focused on an amendment which supports the withdrawal agreement, but only if the Ireland backstop is “replaced with alternative arrangements to avoid a hard border”. This wouldn’t be binding, and won’t pass unless the government or the official opposition support it, but its significance will be as a show of strength on the Tory back benches.

Clever people think that if this amendment attracts a lot of votes it will strengthen the prime minister’s hand in going back to Brussels to ask for changes. Olly Robbins, May’s chief negotiator, is said to have drafted nine options for trying to make the backstop more palatable to Tory MPs who find it so objectionable they would rather leave without a deal.

I don’t see how this can be done, but perhaps there is a form of words that can bamboozle the DUP, Tory MPs and EU leaders at the same time. You wouldn’t have thought that renaming the backstop and calling it “alternative arrangements” would be enough, but maybe that is what the prime minister meant when she told cabinet this week she would have to “present a changed backstop” to get her deal through Commons.

But the two amendments operate against each other. If Cooper-Boles is passed, it takes the pressure off the EU to offer changes to the backstop. The EU would rather agree to an extension of the Article 50 deadline than reopen negotiations on the withdrawal agreement.

That would bring us back to the point I made last week: that those who want us to leave the EU, from Graham Brady to Jacob Rees-Mogg on the Tory side, and Caroline Flint on the Labour side, would then have to choose between the prime minister’s deal, possibly with the most unconvincing of cosmetic changes to the backstop, and postponing Brexit. They know that, once postponed, Brexit may never happen. That final vote on the Brexit deal would be the most historic and critical of all.