I know about that, which sorta validates the gp post. This isn't a EU thing but UK-France thing which shouldn't matter if the UK is or is not in the EU and France threaten to cancel the agreement if the Leave campaign wins.
It seems it matters. It seems that having a hugely conflicting refugee camp in your territory is something you are prepared to do for a close ally, but nothing you will risk for a comercial partner.
The EU was more than a market for the UK. You'll eventually see that.