"... they’ll carry on working, albeit by a different route. "
Yes of course they will, naomi. But they should not have to. Calais is the principle port from the Continent to southern England and as I said, some 5,000 lorries a day use it. It is not alarmist to suggest that should the port become severely disrupted (as it has been on a few occasions in the past months) that chaos will descend onto both the UK and France. (Just see what happens when French fishermen blockade the port for a day).
I have not been to Calais since last summer (and have no plans to go there in the near future, more's the pity). The last time I was there (and I'm sure it's now much worse) the area surrounding the port was like a war zone. There were illegals hanging about on every corner and roundabout, I saw a group of about thirty of them attempt to storm the main entrance, many areas on the outskirts of the town were a disgrace.
Many hauliers are now boycotting the port (and there are plenty of reports - not only in the Daily Mail - providing details). This is bound to cause unnecessary strain on the country's logistics. Huge amounts of goods arrive (and, don't forget, depart) on the Calais-Dover route.
It's no use saying "we should be more self-sufficient". We're not and one of the reasons we are not is because the European Dream has led us to believe we are all one big happy family and can borrow a cup of sugar from next door whenever we run out. That's not much good if aliens are blocking the neighbours' doorstep.