Senior government figures believe they are on the cusp of achieving a breakthrough with Emmanuel Macron on a deal that would see France take back at least some of those who have crossed the English Channel on small boats.
In return, the UK would take asylum claimants from France who wish to come to the UK and are believed to have a legitimate reason to do so.
It’s being called a “one-in-one” out deal, although the numbers will be greater than that.
But the key word to watch out for, when the deal is announced later, is “deterrent”.
Sir Keir Starmer has said both he and the French president agree on the need for “a new deterrent to break the business model of the gangs”.
The big question is the extent to which what is agreed to amounts to that, particularly in the short term.
Will it put people off getting in a small boat?
The pilot scheme is expected to involve around 50 migrants a week being returned to France, in return for the UK taking the same number of asylum seekers in France who are deemed to have a legitimate case to move to the UK.
Critics, including the Conservatives, say this would amount to about 5% of those who are attempting crossing currently, and so would be an inadequate deterrent.
The Tories point to the deterrent they planned but never got started – the idea of sending migrants to Rwanda. This scheme was scrapped when Labour won the election.
But it is true to say this agreement, albeit limited in scale initially, marks a new moment in Franco British diplomacy on this issue – the willingness of France to take back some of those who embark on the cross Channel journey.
The test, in the months and years ahead, can it be scaled up sufficiently to make a noticeable impact on the numbers?
Or, to put it more bluntly, do the numbers attempting a crossing start to fall, or not?
Because unless they do, the scheme, on this side of the Channel at least, is likely to be seen as a failure.