In her letter to Donald Tusk, the European Council president, May expresses the hope that she and Corbyn will agree “a single unified approach”. But I doubt they will agree a blueprint they would both recommend to the commons. So far, May has not moved much, and has mainly reprised the arguments for her withdrawal agreement.

The most likely outcome is May putting what she calls “a small number of clear options” on the future UK-EU relationship to the commons. She hopes Corbyn will sign up to the list and that both leaders would be bound by the decision of MPs. I doubt Corbyn will go that far. He does not want to co-own Brexit. Stand by for the blame game, with both party leaders pointing the finger at each other for not reaching an agreement. Indeed, it has already begun: Geoffrey Cox, the attorney general, has warned that a longer extension to the Article 50 process will be needed if no compromise is reached with Labour.

Although Labour insisted on putting a referendum on the table in the talks, that does not mean Corbyn is committed to one. On Monday, at the very moment Sir Keir Starmer, the shadow Brexit secretary, was telling MPs he supported a confirmatory referendum on “any Brexit deal”, Corbyn qualified that in a letter to Labour MPs. He supports a confirmatory public vote on May’s agreement and as a means of stopping a no-deal exit, but not on any deal. Starmer’s approach is shared by Tom Watson, Labour’s deputy leader, and Emily Thornberry, the shadow foreign secretary and an important swing voter in the shadow cabinet.

Corbyn has done an infinitely better job at masking Labour’s deep divisions on Brexit than May has done on her party’s splits. But his juggling skills are now being severely tested, as he comes under intense pressure from both sides of the referendum argument.

May remains implacably opposed to a Final Say vote. She has already upset many Tory MPs by wooing Corbyn, considering a customs union and admitting in her letter to Tusk that the UK will have to hold European parliament elections on 23 May if an agreement is not approved by then. Backing a referendum would add insult to injury.

But May is also under pressure to move. Philip Hammond, the chancellor, and Jeremy Wright, the culture secretary, raised the prospect of a confirmatory referendum at the cabinet’s marathon session on Tuesday. I’m told that several more cabinet ministers might support one in some circumstances, including Amber Rudd, David Gauke, Greg Clark and David Mundell.

So, despite repeatedly being written off, a Final Say vote is still very much in the game. A confirmatory public ballot was defeated by 292 to 280 in the indicative votes held on Monday. Only 14 Tory MPs supported the proposal, after a heavy whipping operation and the cabinet being ordered to abstain.

There is not a majority yet, which is why the People’s Vote campaign is not keen to see a referendum put to MPs after the May-Corbyn talks. May hoped to do this before Wednesday’s EU summit, though that looks optimistic now. After failing to secure approval for a deal for almost three years, it would be crazy to rush to a final judgement in three days. The suspicion, as one campaigner put it, is that May and Corbyn “might put a referendum up in the hope of knocking it down”. In other words, if MPs rejected the idea next week, the two leaders would take it off the table.