Potential hidden red flags include outstanding finance and even thefts.

More than half of used cars are hiding dirty secrets such as outstanding finance or insurance write-offs, according to new research.

The RAC’s sample of more than 32,000 history checks on separate vehicles found that 52 percent of used cars were hiding “red flags” that should “make prospective buyers very wary”.

More than a quarter (27.5 percent) of those issues were number plate changes, which the RAC says is often down to a previous owner applying personalised registration number. However, the organisation also warns that it could signal a more unscrupulous owner’s attempt to hide the car’s identity.

Old UK car number plate

However, more than a sixth (17.6 percent) of vehicles checked had outstanding finance, which the RAC says should be a “huge red flag” for buyers. Assuming the finance in question is a personal contract purchase (PCP) or hire purchase (HP) agreement, that would mean the cars are still technically owned by the finance company and cannot legally be sold.

Of equal concern, however, is the fact that 14.2 percent of the vehicles checked had been written off by insurance companies, while 1.9 percent were imports that required additional paperwork before they could be sold. Possibly the most worrying statistic, though, was that a handful of vehicles were listed as stolen (0.2 percent) or technically scrapped (0.1 percent).

Yellow excavator loads car in the scrap yard

RAC Motoring Services spokesperson Francesca Mann said vehicle history checks were a vital tool for used car buyers.

“Drivers might be alarmed to see just how many vehicles for sale have hidden histories that could end up costing them dear should they decide to go ahead,” she said. “But this is precisely why we make these checks in the first place – to give them the information they need to make the right choice.

“Forewarned is forearmed, and drivers that do their homework on vehicles put themselves in a much stronger position to negotiate on price, or simply walk away from the sale if they feel they are taking too great a risk. This is particularly relevant this time of year, as the arrival of 19-plate vehicles sees a rise in drivers seeking a good deal on used cars.

Couple buying new car shaking hands with salesman at car dealership

“We recommend every buyer insists on a comprehensive history check for any car they are looking to buy – they should ask to see one if buying through a dealer, or get their own if trawling used car advertisements. Drivers looking for extra peace of mind before purchasing should consider the benefits of having the car professionally inspected.

“Of course, it is important to remember that red flags around things like a number plate change don’t necessarily signal bad news - this information allows buyers to speak to the seller and make sure nothing is awry. However, when it comes to things like discovering whether a vehicle could still belong to a finance company despite being advertised for sale, it’s clear a history check could make the difference between a really good buy or a really bad one.”