fall off (the back of) a lorry (of goods) be acquired in illegal or unspecified circumstances.
☞ The traditional bogus excuse given to the police by someone caught in possession of stolen goods was that the items in question had 'fallen off the back of a lorry'.
1991Time Out People buy so much stolen stuff that … you can … buy a video in Dixons and take it round the corner to a pub, say it fell off the back of a lorry and get 50 quid more than it cost you.