At the ports of Calais and Dunkirk the security checks are carried out by a private security company (French) the heartbeat monitor is the sheds isn’t even used some of the time, and isn’t reliable either, or the muppets who operate it haven’t a clue or aren’t interested , the next check is UKBA passport control, and finally the check with the dog in the lanes, if the dog detects them you get fined as ukba claim that you have entered GB 
rarely UKBA will select you for an xray scan at dover
a similar situation applies a the euro-tunnel in France they too have both ukba and private security x ray scanners /sheds and once you have passed the passport control and illegals are found you get fined
I have parked at transmarck recently without issues,(I don’t recomend it though unless you are empty or have a load that is easily checked , pidou is probably the worst place to park, or stop to buy beer etc, unless you are on yer way out of course , then you just take them as far inland as poss 
talking of the pick nick/lay by and cottaging areas being closed many along the A26 and A1 are closed too