John Bercow has ruled out an amendment that would have blocked the government from spending money in the event of a no deal Brexit without Parliament’s consent.

The amendment, had it passed, would have prevented the government spending money across the departments of Education, Work & Pensions, Housing and Local Government, and International Development. After MPs narrowly voted against a motion tabled by Jeremy Corbyn that would have given MPs control of the legislative agenda in order to prevent a no deal Brexit, backbenchers have no obvious direct way to prevent a no deal Brexit – they could only find means to discourage it, such as the Grieve-Beckett plan to bar the government from spending any money in the event of a no deal Brexit.

Now that method of discouraging a no deal Brexit is off the cards, too. So what’s left? MPs will hope that they can find some other means of preventing a no deal Brexit, but it increases the prospect that there will be just one way route available: a motion of no confidence in the government.

A no confidence motion could prevent a no deal Brexit because, under the Fixed Term Parliaments Act, once a no confidence motion is lost, MPs have 14 days to declare confidence in a new government or an election is triggered. The obvious and easiest way to prevent a no deal Brexit would be for MPs to vote down a government committed to no deal, and then to vote confidence in one led by some political veteran in order to seek a further extension before voting that same government out of office in short order.

But even that route is fraught with obstacles. The biggest problem is that the various parties who want to stop a no deal Brexit will find it hard to pick a candidate to be their Prime Minister designate. It is politically fraught for Labour or SNP MPs to back a Conservative, even one who has been confined to outer darkness like Dominic Grieve.

As for Liberal Democrat MPs, that party cannot undertake that course of action without it passing through the party’s democratic structures. Any power-sharing accord must be approved by the parliamentary party in both the Commons and Lords, the federal policy committee and federal board. While ultimately the party will do almost anything to prevent a no deal Brexit, it adds a further degree of complexity to any negotiation about governments of national unity.

That government cannot be led by any Labour politician who intends to return to frontbench or active politics after, which essentially rules out anyone with close ties to the Labour leadership. And now that the Liberal Democrats are doing well in the polls again, turning to Vince Cable is not a tenable option for Labour or the Greens either. And all of these presupposes that you can get enough support from Conservative MPs to vote against their own government, which is a planet-sized if in of itself.

It is, however, the only immediately obvious constitutional path to prevent no deal. But that it has quite so many moving parts and so many factions to appease for it to work highlights why the possibility of a no deal Brexit remains a real one.