More than a million people think they may have been mis-sold car finance – with an average 30,000 drivers a day having submitted a complaint letter for compensation in the last month.

Consumer website MoneySavingExpert says 1,080,000 claim letters have been produced since early February when it launched its car finance tool to help people concerned they’d been mis-sold – numbers founder Martin Lewis is describing as ‘staggering’.

In January 2021, regulator the Financial Conduct Authority banned something known as ‘discretionary commission arrangements’ that stopped lenders allowing car dealers – or brokers – to increase the interest rate on a car finance deal in order to earn more commission from the sale.

But drivers who had agreements before 2021 could be owed money if an official investigation currently delving into the practice finds customers were charged too much for their car loans because of hidden commission arrangements.

The FCA confirmed in January this year that it was launching an investigation to review historical motor finance commission arrangements and sales after increasing numbers of complaints by customers about commission arrangements made before its ban was put in place.

The results of the probe are expected on September 25.

If commission arrangements are found to have been at fault, the FCA has previously said it will establish a way to compensate people who had a loan affected by the practice.

On February 6, website Money Saving Expert launched its own tool to help drivers, concerned they were affected, formulate and log their own letters of complaint.

MSE estimates around 40% of car finance deals arranged between 2007 and 2021 had Discretionary Commission Arrangements but without checking with loan providers, drivers will not know if it happened to them.

Martin Lewis, founder of MoneySavingExpert.com, is encouraging anyone who had a car finance deal to explore whether they may be affected and if so, put together a complaint letter so that their case is logged.

He explained: “Even though we were at the vanguard of PPI and bank charge reclaiming, in terms of numbers of complaints, this feels like it is building up even more quickly. In value terms, car finance mis-selling is potentially going to be the second biggest reclaim payout in UK history – possibly over £10bn repaid – which could even provide a fillip to the economy as PPI did.

“And it’s because we don’t know what the FCA will say in September that eligible people should look at logging a complaint sooner not later – as the unknown means there’s the risk people may be ineligible if they wait to claim. The regulator’s own website information indicates timing may be an issue and says ‘so, if you think you could be running out of time, you should consider complaining to your provider now’.”

Could I be owed money and how would I claim?

The tool on Money Saving Expert – can help people draft an email should they want to find out more about the car finance agreements they once had in place. It should, says MSE, also help people avoid firms offering to help on a ‘no win, no fee’ basis.

Drivers will need to have bought their vehicle, and arranged their finance, before January 28, 2021 to be considered eligible for any payout should the FCA investigation find in drivers’ favour later this year.

To use the MSE tool, drivers will need to answer a few questions on their car finance agreement – or agreements – before the system builds an email to request information on whether you had any DCAs and then logs the complaint.

This applies to people who bought a car, van, campervan or motorbike on PCP or Higher Purchase deals (not leasing) for primarily personal use between April 2007 and January 28, 2021.