Mr McS: I also agree with Mr Balfour and, if anything, the French ports will be in a worse situation than we will be - the UK could come up with unilateral whizzo wheezes, whereas the French will be governed by what the Union Customs Code stipulates, customs being predominantly an EU competence, and not (contrary to what some UK parliamentarians say) a national one. The source document being quoted is here:
http://data.parliament.uk/writtenevidence/committeeevidence.svc/evidencedocument/treasury-committee/hmrc-annual-report-and-accounts/oral/70147.html and you will see the point being made that there are no 'life after Brexit' negotiations going on at the moment because they're still at the 'divorce' stage.