Ah, yes, it's the blue collar workers who take a bit under the table, and their customers who enable them, who are the real problems.
Because of this, rich assholes must hide all of their money, because fairness. If only the plumbers could set a better example...
In truth, of course, there are good reasons plumbers would prefer to be paid in cash aside from a desire to avoid paying taxes. A big one being that nobody in the UK has checks anymore.