Section 27 of the Hire Purchase Act 1964 was embodied in S27 of Schedule 4 of the CCA 1974.

If you look up the CCA 1974, scroll through the contents right down to Schedule 4 (Minor and Consequential Amendments). Look in Part III Section 27 and you will find the words under subsections 1 and 2:
27 Protection of purchasers of motor vehicles.

27(1)This section applies where a motor vehicle has been bailed or (in Scotland) hired under a hire-purchase agreement, or has been agreed to be sold under a conditional sale agreement, and, before the property in the vehicle has become vested in the debtor, he disposes of the vehicle to another person.E+W+S+N.I.
(2)Where the disposition referred to in subsection (1) above is to a private purchaser, and he is a purchaser of the motor vehicle in good faith without notice of the hire-purchase or conditional sale agreement (the “relevant agreement ”) that disposition shall have effect as if the creditor’s title to the vehicle has been vested in the debtor immediately before that disposition.

There is case law and precedent already. Here's just one example though it is slightly complicated by an Assignment Agreement and a Sub-Hire Agreement.
In effect, the finance co bought the car (a brand new Mercedes so not cheap), and HPd it to a fleet co, who then HPd it to the customer (the sub-hire). The fleet company didn't pay the HP company so they came and repo'd it and the innocent buyer sued the HP company (who he had no contract with) and won.

http://www.wragge.com/analysis_5647.asp