I'm a former drug addict and I have been locked up twice because of my addiction. Nobody's fault but mine.
I was a IV user and getting my hands on gear in prison was no problem. I did my turkey, moved on to another wing and put my feelers out. In less than half hour I was sorted and tooted some gear that very night. 
My girlfriend was always targeted on searches because I was a drug user. She never used drugs, did not even smoke cigarettes. 
The dog sat at the side of her a few times and we were put on closed visits. She had nothing on her by the way.
Drugs shouldn't be available to score in prison. I did the courses required of me and gained some qualifications but I was still a druggie in prison. I was locked up because I needed money for drugs. The judge was right sending me to prison but throughout my prison sentence, I was still using so the punishment was a waste of tax payers money. The system took me off the streets so I couldn't score drugs and be a menace in society but then I went to a place living with a group of druggies and used inside anyway. Irrespective of whether I passed exams and did well in course work, I still wanted drugs in prison and I got drugs in prison. 
I read the post about a visitor being searched and degraded. I am of the understanding that HMP Low Moss is a Scottish Prison but if they executed a drugs bust during visiting hours, the prison must have a problem with drugs. 
Searches have to be done but I take issue with undignified action being taken by the Prison Service and the Police on the base of a dog. Dogs get it right and they get it wrong. I've witnessed it and no dog handler can blag me otherwise.
If drugs are available in Her Majesty's Prison, someone isn't doing their job. I would like to write a lengthy post on what I think if I may?