Mr Red. Both the UK and Ireland are outside the schengen area and have been since it's inception. As a result this requires border checks for both people and goods. As the landing port of Purfleet is predominantly, if not exclusively, for ro ro traffic, goods checks would be perfunctory. If a member of Schengen there would be no checks at all. Trying to use brexit as a scapegoat simply does not fly. If anything checks post brexit would become more thorough and may perhaps of prevented or reduced the scale of this tragedy. The authorities have been warned previously that smaller ports and refrigerated containers would be targeted by people smugglers. The only way to prevent such tragedies is to thoroughly inspect all trailers at the point of embarkation, and accept the concomitant delays and additional staffing required.
https://www.irishmirror.ie/news/irish-news/evil-trafficking-gangs-have-used-20710175
https://www.breakingnews.ie/world/number-of-migrants-smuggled-into-uk-in-containers-on-the-rise-959236.html


https://ukandeu.ac.uk/the-uk-and-the-schengen-system/

The only sad lesson that comes from this is that the unfortunate migrants must detest the EU, and like Brexiteers, regard Great Britain as the land of milk and honey. Otherwise why make such heroic efforts to escape the EU's evil clutches?