Now this is curious . . . “Brexit would have ‘consequences’ for the migrant question, [France President] Hollande warns.” This comes right when French authorities have just wiped out about a quarter of the infamous “Jungle” camp of migrants at Calais trying to get into the UK – and just as British Premier David Cameron went to the northern French city of Amiens yesterday to visit with President Hollande, Premier Valls and other officials.

What “consequences” could President Hollande have meant? Unfortunately, the Le Huffington Post story is not exactly clear. Here is what Hollande said standing next to Cameron at their joint press conference:
One should not raise fears, but speak the truth. There will be consequences if the United Kingdom quits the EU . . . including the manner of managing situations in the matter of migrations.
And here is Premier Manuel Valls:
The day that this relation [that between the UK and the EU] is broken, the migrants will be no more at Calais.
HuffPoFR reporter Alexandre Boudet then helpfully adds, “In plaintext, the doors will be thrown wide open for them rejoining the United Kingdom.” (Wait: RE-joining?)
And then Harlem Désir, French Secretary of State for European Affairs:
There is no blackmail, nor threat, but it’s true that we cooperate more easily as members of the EU than if the United Kingdom wasn’t that anymore, because for example we also work with common European tools such as Europol or the Schengen information system. Even though Great Britain is not a member of Schengen, it cooperates through this system and other means of exchanging information.
Still not very clear. And there still seems to be some element of threat, despite M. Désir’s denials. Luckily, this piece also references an article in the Financial Times (EN-language; but paywall) which helps to clear things up:

Mr. Macron [that’s the French economy minister] said that Brexit could scupper a bilateral deal with France, known as the Le Touquet [A]greement, that allows Britain to carry out border controls – and keep unwanted migrants – on the French side of the Channel.
Finally the picture comes clear as to how, as David Cameron has also been warning his constituents, that “Jungle” over in Calais could potentially move across the Channel if Brexit were to occur – despite the best efforts of UK authorities. For when their officials can no longer first check travelers’ papers on the far side of the English Channel, then they have to do it once they are already in England – and what can you do then with those who you discover don’t belong there, who immediately claim asylum? According to the 1951 Convention Relating to the Status of Refugees, you have to deal with them in a humane way, which includes not just sending them back somewhere, at least not at first.*
Still, this key “Le Touquet Agreement” is a bilateral agreement, i.e. not something within the legal framework of the EU. Therefore, it does not logically follow that it should necessarily fall by the wayside should the UK no longer be an EU member-state. Rather, if that does happen, then that will amount to the French government canceling it after Brexit out of sheer vengeance. If this really is being contemplated, it could set a pattern, by which I mean: If the French will be vengeful after a Brexit, then why won’t the EU be so as a whole? How can those who advocate Brexit really be so sanguine that the UK will be able to re-negotiate basically the same terms for trade, etc. that it had as an EU member once it is out?
One can look at the matter that way, or one can employ another perspective: That, starting here with President Holland and his top officials at this UK-France summit, a campaign has begun of threats and intimidation to try to head off a Brexit. Here at EuroSavant we view the UK remaining an EU member-state as a no-brainer – there’s little doubt future blogposts in the run-up to 23 June will faithfully reflect that – yet one can doubt whether this sort of tough approach is really best calculated to aid the British electorate to make that correct choice when they are called upon to cast their votes.
Anyway, that HuffPoFR piece also reported that President Hollande made special mention of the problem of reuniting the many refugee children stuck at the Jungle who have relatives already in the UK with those relatives. David Cameron was said to be accommodating on that. Further, Cameron announced a supplemental payment to France of €20 million to help out with those refugees still stuck at the Jungle – mainly, however, for encouraging them to be dispersed and moved away to other parts of France.
* Note that the “Le Touquet Agreement” has to do with people arriving to the UK via the cross-Channel ferries. There are analogous agreements (which are also bilateral), under different names, covering train (Eurostar) and aircraft travel, which also could be abrogated by the French/Belgians (train) or those and other EU member-states (aircraft) in the event of Brexit.