I'm not a fan of most of the British government's advertising efforts that we get bombarded with regularly, most of them seem more aimed at convincing potential voters that the government is doing a good job (i.e. effectively a government funded advert for the Labour party) rather than having any positive effects (especially the "we're closing in series").
To its credit this latest effort doesn't seem to be in that mould and is actually aimed at reducing the numbers of people drug driving. The downside is that it is mindblowingly stupid. Here it is from youtube for those lucky enough to have escaped seeing it.
As I said, on first watching I was vaguely pleased that at least it wasn't a covert Labour PPB. Then another thought struck me, the message that you get from that advert is not "don't drug drive". What you get is "here's how the police might spot that you've taken drugs" and what this leads on to is the obvious strategy of: if you have taken drugs and there's police around then don't let them see your eyes. Whether that's not staring at a police car as it goes past or not looking them in the face if they're talking to you for another reason.
In short not only is the advert unlikely to stop people drug driving, it's going to help them avoid detection for it. I don't know what the creators were on when they dreamed this up (all bad puns are as ever completely intentional) but hopefully they'll think their next advert through properly.