The Financial Conduct Authority could implement a simplified claims process if it deems there has been widespread unfair treatment of car buyers due to discretionary commission agreements between lenders and car dealers or brokers.

Its decision to review historic commission arrangements could open the floodgates for millions of consumers who have used and new cars in a 15 year period to lodge complaints and seek compensation from motor finance houses such as Black Horse and Barclays Partner Finance.

Sheldon Mills, the FCA's executive director of consumers and competition, told BBC Breakfast that the regulator could have two options: one is to give more guidance to car loan firms to help them deal with these complaints efficiently and consistently, and the other is to implement a scheme in which anyone who was affected gets some compensation if they are entitled.

The FCA has some experience of such measures. After it identified widespread misselling of payment protection insurance (PPI) it introduced rules to help people get fair treatment and ran national marketing campaigns to encourage complaints to be submitted before its 2019 deadline.

On the latest motor finance issue, Mills said: "Three quarters of the loan agreements between 2007 and 2021 would have had some form of discretionary commission model, so there will be millions of agreements or potential claims.

"It doesn't mean that every one, though, is entitled to compensation.

"That's why we've decided to do this review of historic agreements to assess the size and scale of liability, and then look towards whether we put in a scheme to compensate people."

He said, until now, most consumers will not be aware of these discretionary commission models and the law allows them three years from the point they became aware to make their complaint. "There is no rush."

Mills also emphasised that people do not need help to make a complaint, such as that offered by claims management companies. Rather their motor finance providers will be able to help them with their complaint.