It might just be the tip of the iceberg, for all we know.
Most vehicles just rumble through, and the Police and border agents would need plenty of sniffer-dogs to do the job thoroughly, and no-doubt more personnel too.
I recall emailing Mr. Elphicke proposing that the Government put a 1 pound extra fee on vehicle traffic passing through Dover Port in order to use the money to increase security. Nought came of it.