Which is why you get handcuffed and not allowed to use your phone. You think you're being big and clever but if the phone contained evidence you'd be looking at

Which is why you get handcuffed and not allowed to use your phone. You think you're being big and clever but if the phone contained evidence you'd be looking at attempting to pervert the course of justice (cf Rebecca Brooks right now). Pretty much every police van already has constantly running video, all the custody areas of police stations do. And unlike the US that video doesn't get "lost" if you make any complaint.