Theresa May really could face a leadership challenge from Brexiteers if she doesn’t deliver on the customs union

The government will lose a vote for a soft Brexit on Thursday, but the prime minister has no choice but to talk tough and carry on

Theresa May is going to refuse to play on Thursday because she knows she is going to lose.

Conservative MPs will be told not to vote that day on a motion demanding a softer Brexit, tabled by Nicky Morgan and Yvette Cooper, the Tory and Labour former cabinet ministers.

This is leadership by abstention, and it is part of a pattern. Last week May refused to recall parliament to vote on air strikes in Syria because she thought she might lose. This time is different because there will actually be a vote and the government will lose it, but if most Tory MPs don’t take part it is easier to say the vote doesn’t count.

This tactic of not taking part in votes is one of those gradual changes in the flexible British constitution that got going under David Cameron. The convention used to be that if the government lost a vote it was embarrassing, and the prime minister was expected to respond. Now there is a lot of theology about binding and non-binding votes, and if the government looks likely to lose a non-binding one it simply refuses to take part and ignores it.

Thursday’s motion calls on the government to make a customs union an objective of its Brexit negotiations. It is indeed not binding, but the demand won’t go away because there is a majority for it in the House of Commons. It may seem a technical question – it would mean no customs checks on trade with the EU, though it would restrict our ability to sign trade deals with other countries – but it has become the pressure point.

There is no majority in the Commons for stopping Brexit, or for keeping the UK in the single market, because that would mean accepting the free movement of people. But there are more than seven Tory MPs who support a customs union, which is all that is needed to overturn the Tory-DUP majority.

Hence the threatening noises coming from hard Brexit Tory MPs. Paul Goodman, editor of Conservative Home, reports one saying: “If there’s a cave-in on the customs union, I think there will be a leadership challenge.” Normally, you wouldn’t pay too much attention to anonymous backbenchers, and Goodman himself says: “Perhaps it’s just talk: after all, there was talk of a challenge to David Cameron for most of the coalition years.”

But Goodman is a good judge: these things can happen by mistake. It doesn’t make much sense for the hard Brexiteers to try to bring down May, because they may not succeed. If 48 of them trigger a vote of no confidence in May, she could win it. If they do succeed, her replacement would face the same majority for a customs union in parliament. The only difference would be if they thought May was about to betray them by giving in to it, whereas Michael Gove, say, might stand firm. But a leadership challenge is a hazardous enterprise, and they can’t guarantee who they would get.

One reason for taking the possibility of a leadership contest seriously is that hard Brexiteers can count, too. They know that if the soft Brexit majority can find a way of forcing May’s hand, she might well cave in. If there were a way of dressing up a customs union in May’s language of a “customs partnership”, she might bolt for it, late in the negotiations.

The House of Lords can see it, which is why there was such a large majority to defeat the government in the vote on a customs union last Wednesday. It merely required the government to say what it is doing about a customs union, with which the government can comply by saying “nothing”. But this was designed to urge on the like-minded majority in the lower house.

The EU negotiators can count, too, which is why they rejected May’s plans so emphatically on the same day, saying: “None of the UK’s customs options will work.” It looks as if Michel Barnier is trying to box May into a customs union or nothing. Although he cannot negotiate directly with the House of Commons, he knows that May’s position is precarious.

Theresa May can still pull this off. The point at which the soft Brexiteers might be able to secure a customs union is when parliament finally votes on the terms of the exit deal in October or November. If a last-minute renegotiation is needed to save the deal, then she might go for a customs union by another name. By then it would be too late for the hard Brexit crowd to bring her down.

The trouble with this plan is that, if the soft Brexiteers, the Lords and the EU can work it out now, then so can the hardcore Leavers. That is why May has to talk tough and play for time. If 48 hard Brexit Tory MPs think she is going to sell them down the river, Graham Brady, chairman of the 1922 Committee, could suddenly be on TV announcing a vote of no confidence in the leader. It need not be a co-ordinated plot; it could be the accidental product of fear and mistrust.

Which is a complicated way of saying that I have no idea what is going to happen.