
I'm none too certain what a "plant passport" is but suspect it's along the lines of a phytosanitary certificate: a piece of paper issued by the agricultural authorities in one country assuring the agricultural authorities in another country that a certain specimen of a certain plant is free of pests and diseases.
Used to be these were easy and cheap to get, so individuals found it practical, for example, to import plants from the UK into Canada, from the US into Canada, and so on, in complete conformity to the law.
But the "user pay" concept took over, the fees rose to prohibitive levels, and those days are now past. This application of "user pay" overlooks the fact that it's in everyone's interest to keep out plant pests and diseases, not just the importer who desperately wants a specimen of the double-flowered, silver-variegated form of /Veriolitsis glomulama/, the better to indulge in gamesmanship with his fellow plant nuts.
Gardeners, however, are as a class criminals and have never let anything as simple as a missing piece of paper stop them. The rise in fees has the net result that more plants are smuggled without inspection than ever before.
[Aside: phytosanitary certificates issued by China are, as you would expect, worthless. A small bribe is all that is required to get one, evidently, regardless of the subject plants' health.]
As for the Colorado potato beetle, it's a serious pest and one that's been the subject of serious efforts to block from the UK. But laws to facilitate this have been on the books a long time: probably things like mandating reports of any infestations found, and so on. Look at how the hoof & mouth disease outbreaks in Britain have been handled for an example of how this works.
And, moreover, no thinking citizen would disagree with a law giving entry in pursuit of a Colorado potato beetles.
At one time, the theoretical view of the law was that statutes merely gave voice to what everyone agreed was the law: no raping, stabbing, killing, stealing, etc. NuLizar (hail our Lizard Overlords) doesn't understand this bedrock conception, and thinks they can pass laws to institute their personal silly ideas.
Just as Monte Python had silly walks, so NuLizar has silly thoughts.
Gordon Brown & Jacqui Brown in a Punch & Judy show, anyone? Or have P&J shows been outlawed as tending to encourage violence among the young? (As thought without them Britain is an utterly peaceful place where no one does anything awful to anyone else.)
Better stop; I'm starting to rant. Please forgive me, O Divine Moderatrix!