My reading is that it’s not that they drank some at some point in their lives, it’s that they drank it shortly before they committed the offence that got them imprisoned.
Therefore possibly showing that drinking Bucky is doubly unwise in that it makes you more likely to commit an offense and that it makes you more likely to do it in a way that gets you caught.
Or alternatively that people who regularly drink Buckfast are people who through a combination of reasons have poor decision making and impulse control while lacking the funds for decent scotch.
