What's the issue?
AC (12.20) wrote: "if my reading is correct, then the police have talked sense....and el reg has jumped on the story because the quote contained the the text 'DNA'...."
Not quite, although I appreciate why you and one or two others have said this.
When I read the release, I thought that the way the sentence was structured, a PR COULD argue that a totally literal interpretation of that sentence was as you have suggested.
However, there are two issues with this reading. First, it merely pushes the issue one step further back: if being DNA tested is not career-damaging, but being arrested is, then that is equally wrong.
However, there is also the textual crit perspective to have a go at. It is fairly clear that this passage is intended to warn people off mere possession of a substance, even if possession is legal. It is police going beyond simple "enforce the law" territory into something else.
The language is fairly oppressive: you will be "taken to a police cell" is clearly there to emphasise the heaviness of what may happen. Then DNA. And to cap it all, there is going to be a consequence to the arrest (of which the cell-holding and DNA stuff is a part).
SO I am less certain that one can exculpate the police quite so easily.
If you want my honest view of what is going down here, I think that someone middle-ranking realised that they could not brandish the law...so decided to shift into threat territory without thinking first: without thinking that their remarks might have consequences in respect of other policy issues.
This whole set-up seems difficult to me. As others have observed: if you are found in possession of a bag of white powder, chances are, the police would (rightly) want to know more. Happened to a (medical) friend of mine many years back when he was caught cycling round Cambridge in possession of a back of aspirin powder.
But just rethink that particular section.
How would you react if the police issued a warning as follows.
At halloween, people have been known to wander the streets carrying flour. This is a white powder and, since it COULD be a drug, anyone found in possession of said white powder will be locked in a police cell, have their DNA taken, arrested.
Is that really what we, as a society, want?