Most UK motorists clutter their boots...
From smelly sports kit to half-eaten sandwiches, 35% of drivers say they are happy to let the mess build up and only clear it out twice a year.
But the dirt doesn't put drivers off from letting other people into their car.
A staggering 93% of car owners say the state of their car wouldn't stop them from giving a lift to a friend, taking the kids to school or parking in a posh area.
The survey, commissioned by Kia Motors, explores the filthy habits of the UK's car owners and uncovers the clutter that collects in their boots and back seats.
And the findings couldn't come at a better time, as this week is National Spring Cleaning Week in the UK.
Top of the rubbish pile are clothes and shoes, with four out of10 owners (38%) using their car like a laundry bin, leaving anything from spare jumpers to dirty boots on the back seat.
Messy motorists are obviously not too worried about hygiene when they're on the go - a third throw their leftover food and wrappers on the car floor (31%) and one in 10 let their car ashtrays overflow with cigarette butts (9%).
And if you're wondering what that smell is, then watch out for festering sports bags.
14% confess to leaving their used kit in the car in between trips to the gym.
Despite taking their work home, a third of drivers can't manage to get it through the front door, leaving their paperwork, bills and receipts out on display creating clutter?and a potential security risk.
When it comes to cleaning the outside, car owners scrub up a bit better!
Nearly half those questioned wash their car once a month (46%) and a super-clean fifth of motorists clean it once a week (18%).
Yet there are still those who don't mind a bit of dirt build up - 5% said they'd only clean it once a year and 1% said they'd never washed their car!
A massive 82% of motorists are careless with their music collection, leaving loose CDs and cassettes littering the floor
One in 10 drivers tidy up their car just once a year (8%) and 1% said they'd only clean out their car when they came to sell it!
Women are more likely to leave empty food packaging in their car than men - 36% compared to 25%
Men clean out their car more often than women, with 44% tidying up once a month compared to 38% of the female respondents
Nearly a quarter of men wash their car once a week (24%) compared to only 14% of women
Women would be more embarrassed to give someone a lift in a messy car - 7% said they would refuse to do it if their car was untidy
Paul Williams, managing director of Kia Motors (UK) said motorists should be ashamed at the findings.
"As a nation, we're known for being ?house proud' but we're obviously not very 'car proud'.
"It seems that our motors are showing up the messier side to the great British public! What better time to clear up the clutter than during National Spring Cleaning Week."
To get motorists to smarten up their act, Kia has put together some top tips to a tidier car?
Don't let the rubbish build up - tidying little and often will keep your car clutter-free so keep some handy bags in the car to empty out rubbish
Dust down the dashboard and door panel with a damp towel - it makes the job easier and lifts off those sticky food and drink stains
Use a cotton bud to remove dust that builds up in the air conditioning fans. For the cracks in between the controls, use a toothpick and some tissue paper
Baking soda in the ashtray will keep down the odour of cigarettes and extinguish the butts quickly
A clean, dry paper towel and white vinegar will remove any dirty build-up on the windows. When the glass is dry, polish it with crumpled newspaper as, unlike paper towels, newsprint doesn't leave lint behind and the ink acts as a polish
Avoid washing your car with a hosepipe to save water - use a bucket and sponge instead.
Sticky tape will pick up most crumbs from your carpet and upholstery and save you having to lug the vacuum cleaner outside!