Citroen is recalling more than 20,000 of its C3 Picasso cars in the UK because of concerns the brakes can be activated from the passenger side.
The problem arises because of the way the car is made in France then modified for right hand drive for UK export.
A BBC Watchdog investigation found the brake could still be engaged through a cable under the passenger footwell.
Citroen said although that was a remote possibility, it is offering customers a free modification to the UK vehicles.
The BBC TV consumer programme was alerted to the problem by a Kent-based commercial cleaning company, Town & Country Cleaners, which has three of the Citroen vehicles in its fleet.
The firm only discovered it when one of their drivers travelling at 70mph (112kmph) on a motorway found his car suddenly screeching to a halt.
The programme has since tested two more C3 Picassos on sale at dealerships in south east England - both of which have the same flaw. The model has been on sale in the UK for the last two years.
Motor engineer expert Mark Brown, who examined the cars, found that the braking mechanism underneath the passenger floor was easy to press - as it was only covered with a thin piece of felt.
"It's potentially very dangerous indeed because the passenger wouldn't know he's the one activating the brake. The driver wouldn't know what's going on, and the people behind wouldn't know what's going on.
"I think Citroen should take a good close look at this and seriously consider recalling the vehicles, and fitting some sort of structural permanent cover to protect the braking mechanism."
Tim Shallcross, Head of Technical Policy for the Institute of Advanced Motorists, added: "Citroen must investigate the problem as a matter of urgency. If the driver's control of the car can be compromised, they must take action to modify all cars, via a recall if necessary."
In a statement to Watchdog, Citroen said there had been no reports of the problem before the Watchdog programme, but because of a "remote possibility" it could happen, it announced a recall.
"The recall will require the fitment of an additional component to isolate the braking mechanism from the front seat passenger," the statement continued.
The company said the modification would be free at Citroen dealers.
"In the meantime, C3 Picasso owners should continue to use their cars as normal. Customers wanting further advice or information are asked to call the Citroën Contact Centre on 01753 475862, or to email email@example.com."