That'll be twenty quid then...

If you get a plumber out to unblock the kitchen sink, or a carpenter to plane a bit off an ill-fitting door, or the window cleaner comes round, how do you pay them? Cash, don't you?  I certainly do. What's the alternative?  They have no provision for dealing with debit or credit cards, and may quite understandably not fancy accepting a cheque which might bounce.  So if they then don't declare that money to the taxman, are you in any way complicit in the fact that they are breaking the law?  It is seriously being suggested that you might be.  I think a distinction can and should be made between paying the asking price in cash and deliberately negotiating a cash price ("How much for cash?").  I can't see anything wrong with the former, but the latter may be questionable.