Brexiteers remain adamant they will vote down Theresa May’s deal on Tuesday in order to force a renegotiation with Europe to make the deal more palatable.

As Dominic Raab, the former Brexit secretary, says, the “number one” change that would make the May deal acceptable is an amendment to the Irish backstop that will enable the UK to quit it unilaterally.

This has always been Mr Raab’s position (recall him defiantly demanding a three-month unilateral break clause from the Irish deputy prime minister Simon Coveney) but as a former Brexit secretary, he will know why this is such a tall order to deliver.

Mr Raab says simply that Downing Street must show some “will and resolve” to make the EU change its mind, even though he knows from bitter experience why it’s a bit more complicated than that.

As he well understands, there are three good reasons why the EU did not (and almost certainly will not) give up on the backstop - which are complicated by the fact that there is one hypothetical scenario in which they just might. But first, the three reasons.

Insurance policy

One. The Irish backstop is a ‘mutual’ insurance policy, not something imposed by the EU. It reflects that both sides are committed to the invisible Irish border that is at the heart of the Good Friday Agreement.