Dave:
There are minimum standard of SPS required by WTO. These are substantially lower than the EUs standards, and the country concerned has great flexibility in what it chooses to implement. So I accept that when I said' obligatory' I chose a poor word - the obligatory checks are minimal.

So if, as in 2013, a a Romanian-based slaughterhouse chooses to pass off horse meat as beef in the UK, we are under no kind of obligation to have the checks in place to detect it. Even in 2013, it was Ireland that detected it, but that was a role shared across the EU in several places, Now of course, we have to do it on our own - or not bother, of course.

So in effect you're saying that although the EU have higher standards, they don't enforce them.
Just as well we left ;)

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. (From Wikipaedia)