For example, were I so inclined and we uses your ANPR in urban areas idea, I would simply change vehicle outside the urban area.

Yes, and that is what they do now because the cameras are already in place.
These are smuggling rackets, just a minute proportion of legitimate international trade.

After Brexit legitimate trade will whiz across the border unhindered as it does now. That is all that is required by EU.
May has again stated emphatically that will happen, but EU and Remainers just won't take yes for an answer.