AIUI (which is superficially):
a. a personal contract purchase is a conditional sale and so within section 27 (as amended);
b. a logbook loan (on a bill of sale) ain't. In law anyone who buys a car subject to a logbook loan has no protection from the lender repossessing it at will.
I think HPI check the (High Court?) register of logbook loans, but I'm not sure every such loan is registered. Check with HPI before relying on them (let alone on me!)