Coincidently, juxtaposed people controls get a mention from Mr Gove:
https://www.bbc.co.uk/news/uk-54260470 (same article as RH's) "There also remains a risk of continuing disruption caused by Schengen controls being applied rigorously at the juxtaposed controls at the Port of Dover and Eurotunnel," the document says.
I suppose that's true in the context of a 'reasonable worst case scenario', since the French have been known to understaff controls and to apply them to 100% of freight drivers (as is their right, of course); normally they do neither.