Passing the border without being stopped is not a confirmation of anything, except that Border Force simply cannot check every single vehicle.
Make sure you are not relying on the driver to inform you of a problem (in some cases, he may be involved). Border Force will normally only inform other Government Agencies or third parties if the load is for human consumption. Remember, even then, 90% of the vehicles are unchecked.
We recommend carrying out your own spot checks. Particularly when using sub-contractors.