Van, as a visitor to many UK prisons, I can say that if a visitor refuses to be strip-searched, it cannot be enforced, merely the Visit is cancelled. This situation only arises if the drug-detection dog indicstes that the visitor is carrying drugs, or the Officers suspect it. They can however call the Police, who will arrest the visitor once he/she steps outside the prison gate. The Police have the right to strip-search the suspect at the Police Station. Prison Officers can only strip-search inmates, not visitors. (I must add that I personally never committed any such crimes or carried drugs while visiting!)