Oh but it is a problem, due to the Le Touquet Treaty - that allows UK Customs officials to make border checks on French soil.
As a seperately negotiated agreement that can be terminated at any time by either party with just 2 year's notice, it represents a massive potential curve ball.
If the French do the pull the plug (and they have every right, due to the lack of support over the Calais migrant camps by HM Gov) it WILL be chaos.
And if the Br-idiots think leaving the EU will solve the problem all these frightful illeagals* just wait...
Take it from someone that crosses every six weeks.