So David Gauke thinks that paying cleaners and tradesmen in cash to get a discount is morally wrong. I'm not sure. It seems like this is a very common form of tax evasion, and people know it's a bit naughty (i.e. because it's illegal for the tradesperson to fail to declare the income); but I don't think people feel that they have crossed any sort of moral line.
Is it really a moral issue?