Jo Johnson’s resignation increases the chances of a Final Say referendum by another notch

Jo Johnson isn’t the first minister to resign over Brexit and call for another referendum, and he probably won’t be the last. Phillip Lee, the former youth justice minister, resigned in June.

At the time, Johnson told friends that the only answer to Brexit was to “blow up the whole thing”, but he delayed his attempt to do just that until now, possibly the week before the prime minister finally manages to secure a draft withdrawal agreement.

Theresa May is hoping the wording can be finalised so that the cabinet can sign it off at its meeting on Tuesday, in time for a special EU summit meeting to be held at the end of this month.

But if she can do that, she then has to get it through parliament, and Johnson is trying to rally support for a last attempt to stop Brexit. There are rumoured to be a handful of other pro-EU ministers thinking about resigning. If they go, they will strengthen the resolve of Tory MPs who support a new referendum – only about a dozen have declared their support so far.

What was interesting was the support for Jo Johnson from his brother. Although they were on opposite sides in the referendum, Boris Johnson now says they are “united in dismay” at the prime minister’s plan. That implies that Boris thinks staying in the EU is better than Theresa May’s Brexit – as Jacob Rees-Mogg has said explicitly.

If more hard Brexiteers come to this view, they might switch sides in the House of Commons and support a postponement of Brexit and possibly a referendum. That would complicate the arithmetic no end.

It is already complicated enough. There is a majority among Tory MPs for a soft Brexit. So far it has been assumed that they would support the prime minister’s deal, almost regardless of what was in it. But if she compromises by agreeing an Irish border backstop deal from which the UK is unable to escape, some of them may decide differently. And Johnson’s powerful resignation message may have encouraged some to move towards a Final Say referendum instead.

Then there is the Labour Party, which is likely to split three ways: support, oppose and abstain, but in proportions that are unknowable.

As it is, no one knows what is going to happen. It is not yet clear that Theresa May can secure a deal that would be acceptable to the cabinet and the DUP. It may be that the next resignation will be from the cabinet as she tries to get a draft deal through.

But Jo Johnson’s resignation increases the uncertainty a notch, and increases the chance of a second referendum slightly but perceptibly.