I doubt that anyone who "smuggled" a few sleeves of cigarettes and 20 or so bottles booze back was a major criminal on the other hand if they filled a van full then they clearly were criminals. And when that source of money ran out moving onto people smuggling was an obvious next move. There is not a set limit to the amount of cigarettes or booze you could bring back from Europe, as long as it was for your own personal use. I was stopped with 80 sleeves of cigarettes and they could do nothing about it.
Gang master is not illegal, it's a job description/name of a person who organizes and supplies farm labourers for vegetable crops cabbage, Brussels sprouts etc.
" Transit van running on cherry doing a bit of window cleaning or moving couches for someone is making the odd tenner to keep his family fed" The odd tenner? A bit unlikely it wouldn't pay for the transit van. Do you think everyone working in the black economy is earning the odd tenner? You appear to be implying or assume that the government is using digital payments to catch tax avoidance? People are making the decision to become cashless it just so happens fiddling your taxes is very difficult when everything goes through your bank account.