Given Theresa May’s apparent shift from planning for a hardish Brexit to a softer one – we described what has happened in detail yesterday – you may wonder why Leave-backing Conservative MPs are not in open revolt and planning a leadership challenge. We cited a number of reasons and they’re worth exploring more fully.

First, this change has happened without some of those Tory MPs appearing to notice it. The EU gave ground to the Prime Minister in December’s agreement over money and the role of the European Court of Justice. Seven out of ten of our party member panel approved of it. Many Brexiteer MPs assumed at the time that the “backstop” arrangement over the UK-Ireland border, one reading of which would see Britain bound to the rules of the Customs Union and Single Market for manufactures and agriculture, would never kick in.

The Chequers Summit agreement earlier this year, which foresees a high degree of regulatory alignment in some cases; the transition arrangements (with no repatriation of powers over fisheries during it, and no change to free movement either); the Prime Minister’s attachment to a customs partnership; the likelihood of staying in the Customs union for longer, because systems required to leave it apparently won’t be ready for 2021; last week’s agreement on the backstop – all these various climbdowns, shifts and clarifications have come one at a time, and some Tory MPs don’t seem to have noticed that, taken together, they look a lot like “Norway Minus”.

Second, not all Leave-supporting Tory MPs are opposed to such an “EEA-lite” settlement in any case. The best part of 80 plus of them are on the European Research Group’s mailing list. But not all are agreed on the best negotiation outcome for the UK. Furthermore, there are a further 50 or so Conservative MPs who backed Leave in the referendum and are not ERG members. Some in both camps would be prepared to settle for full EEA membership for Britain in any event.

Third, there seems to be little appetite for a leadership change. Half our panel – and, as far as we can see, most Conservative MPs – want Theresa May replaced by the time of the next election. But a change in Number Ten wouldn’t alter the balance of forces in the Commons, where there is no majority for the “WTO option” (though there may just be one for quitting the Customs Union). Furthermore, a botched challenge might reinforce the Prime Minister’s authority. This is giving some of her critics pause for thought.

Fourth, there is a natural reluctance to do anything that might bring Jeremy Corbyn nearer Downing Street. The point is so obvious as not to need stressing. It is felt particularly by Conservative MPs who are less gripped by the Brexit outcome than, say, Jacob Rees-Mogg or Anna Soubry, and feel that the whole business is doing nothing for the Party other than creating and widening splits. Their cry is: “a plague on both your houses”. This is felt especially stronger by MPs holding marginal seats.

Finally, very many Tory MPs, not all of them Leavers, are waiting for Brexit Day. “Look,” some of them say, when asked about their thinking, “we know that the policy isn’t going in the direction we hoped. We appreciate that Brexit will be less than clean. But the priority must be to get to March 29 intact. Let’s get the EU Withdrawal Bill through – and get out of the EU. Better to have another push for the sort of Brexit we want from the outside rather than the inside. And next summer marks the best time for a leadership change.”

This thinking begs some questions. For a start, there is a chance that the Brexit negotiations collapse, or that May can’t get a Commons majority for a deal, and that a panicked Parliament then seeks to suspend the Article 50 process. Our judgement for better or worse is that the odds against that outcome are very long. It’s more likely that in circumstances that Parliament would seek the equivalent of an emergency transition arrangement while a general election took place.

None the less, one can see the attraction of the case. Get out as soon as possible. And then push for a fuller Brexit later – from outside. This argument will have its attractions for Brexit-backing Cabinet Ministers who don’t want to resign. Some supporters of Michael Gove are making it. It would be surprising if senior Leave-supporting staff in Downing Street, such as Robbie Gibb and Stephen Parkinson, don’t hold it (though they wouldn’t, of course, want a leadership change).

And there is always the human instinct to believe that everything will be all right on the night. We will get a fully-fledged trade deal before next March – or something very close to one, anyway. The backstop will never kick in. We will leave the Common External Tariff. Ireland and the EU will back down on full regulatory alignment. All shall be well and all manner of thing shall be well. “We’re on our way, on our way. / To the Brexit, we’re on our Way. / How we get there we don’t know, how we get there we don’t care. / All we know is that we’re on our way…”