Hundreds of drivers are at risk of being slapped with a hefty £1,000 fine for making a simple admin error, according to experts.
Ripe Insurance found a handful of road users are breaking the rules by not reporting their car modifications to the DVLA.
A survey of 2,000 motorists found one in 25 road users have made a modification to their vehicle.
However, just 62 percent said they have actually told the DVLA what has been changed.
The rules state that the DVLA needs up-to-date records of all cars for tax and road safety purposes.
It means drivers must update the details on the V5C logbook and tell the DVLA if anyone makes changes to a range of parts.
This includes the colour of a vehicle, the engine, its cylinder capacity or fuel type.
Any cosmetic changes to the chassis or bodyshell, number of seats in the car or the weight of a model must also be disclosed.
John Woosey, Founder of Ripe Insurance, commented: “For many people, personalising their car with custom modifications is a harmless passion.
“And the good news is the majority of mods are completely safe and legal. However, amidst the excitement of making upgrades, you must not forget about the necessary admin that goes along with it.
“Our research suggests that there are thousands of drivers on the road right now who are at risk of serious fines because of this relatively minor oversight.
“So, we would urge all modified car owners to double check their paperwork and complete the relevant forms to avoid a potentially significant financial blow.”
Failure to follow the rules could see drivers issued a staggering £1,000 fine as a punishment.
Experts also explain that car insurance cover could be invalidated if motorists keep any modification details to themselves.
Ripe Insurance also warns most updates will likely make a model more expensive to insure.
Some modifications could be illegal and also lead to hefty fines and penalty points issued on a driving licence.
Ripe warns that installing fully tinted windows, loud exhausts or neon headlights could land motorists in serious trouble.
