Allegedly folk are raising money with "logbook loans", then (would you Adam an eve it) they are selling their cars before settling their debts (tut tut).
"These loans, unlike other forms of credit, have been known to leave innocent third-party buyers liable for the previous owner's debts".
According to what I've read, the lender doesn't have to (an often doesn't) place the loan on a register, so it won't come back on any HPI check that's commonly done before buying a car.
I'm not sure if this has been fixed as it is a few years old now.
BBC - Press Office - 5 Live Investigates logbook loan scam