The point I have been making along is that they exploit the difference.

There will not be significant differences on food regulations when we leave.
We already import food from outside EU, where there are big differences, without problems.

We have a food inspection regime which looks at food regardless of its origin, but not at the borders. You have raised an issue which has not bearing on borders or Brexit.
It had nothing to do with membership of EU or border controls.

Wiki,
"In the UK, a House of Commons Select Committee on Environment, Food and Rural Affairs report on the horse meat incident was not critical of UK or Irish producers. It expressed concern that horsemeat contamination was the result of fraud and other criminal activity across the EU. Chair of the Committee Anne McIntosh MP said: “The evidence suggests a complex network of companies trading in and mislabeling beef or beef products which is fraudulent and illegal.”[10][11]
The second major UK report on the horse meat incident was conducted by Professor Chris Elliott, the Director of the Institute for Global Food Security at Queen's University Belfast. In his independent report he argues that food crime was at the heart of the horse meat incident: and made a range of suggestions for how this could be tackled. “Industry, government and enforcement agencies should, as a precautionary principle, always put the needs of consumers above all other considerations, and this means giving food safety and food crime prevention – i.e. the deterrence of dishonest behavior – absolute priority over other objectives."

Nothing to do with membership of EU or border controls.