In Reply to: Fell off the back of a lorry posted by Mark Mywords on April 14, 2010 at 09:36:
: "Fell off the back of a lorry" to describe goods or something that is "hot " ie, stolen or an article or goods that the supplier will be vague about their background or where they came from. Where does this old saying derive from?
It was a way of explaining away the lack of provenance of goods that had been stolen, without admitting their dishonest origins.
The vendor was claiming that he had come upon the goods in a way that could not be traced, but was not seriously illegal: that he had found them after they had 'fallen off the back of a lorry'.