More French cars have been shown to have a flaw where the brakes can be activated by the front seat passenger.
The problem highlighted by the BBC Watchdog programme occurs in some cars made by Citroen, Peugeot and Renault.
The fault arises because of the way the cars are adapted for right-hand drive, leaving a brake mechanism on the passenger side.
Last week Citroen recalled more than 20,000 of its C3 Picasso cars because of the problem.
Watchdog viewers have highlighted related problems affecting eight models - the Peugeot 206 and 307, the Citroen C3 Desire, C3 SX, C4 VTR and C4 SX HDI and the Renault Scenic and Espace.
Motor engineer expert Mark Brown, examining a Citroen car, said: "These models which are built in France were designed as left-hand drives - so the master brake cylinder is on the left.
"To adapt them for the UK market Citroen added a cross bar between this cylinder and the driver's brake pedal on the right but in doing so, they failed to adequately protect the passenger-side lever."
Mr Brown examined three cars, one from each manufacturer, Citroen, Peugeot and Renault, and confirmed all had a similar flaw.
He estimated between 250,000 and 500,000 vehicles could be affected. "In my view these cars should also be recalled," he said.
Since the Citroen C3 recall last week the company said "a very small number" of non-C3 Picasso customers had been in contact.
In a statement to Watchdog, Citroen said: "We will make contact with the other customers who have contacted you, to inspect their vehicles - until we have spoken to them, it's difficult to comment further on any of the points or issues they have raised."
Last year, Peugeot, which is part of the same company as Citroen recalled some of its 308 models with a similar problem.
But in reaction to the latest concerns the company said: "In 2004, the Vehicle and Operator Services Agency (Vosa) tested a 206 following a customer complaint. Vosa concluded that the condition, similar to what has been reported in this programme was to some extent artificial.
"Vosa therefore proposed that a recall was deemed unnecessary but made the recommendation that the company instigated a production change and this was applied at the beginning of 2005, since when we have had no further customer incidents.
"We have had no cases of this type on any other models, which are all different and therefore we would like to investigate further the three cars mentioned in this programme and we will contact the customers directly to organise this."
Renault is advising owners to contact their Renault dealer if they are concerned. It also confirmed it had found a similar problem in some Renault Megane models.
In a statement, Renault said: "We have identified that on some pre-2004 Megane models (registered in 2002 and 2003), under certain unusual and extreme conditions, it is possible to produce a braking effect by applying pressure at the very top of the passenger foot well.
"Any pre-2004 Megane owners who are concerned should contact an authorised Renault dealership who will be able to assess their vehicle to determine if any remedial work is required which will be undertaken free of charge."
Renault added: "As a responsible manufacturer, Renault takes the safety of its customers, and road users in general, extremely seriously.
"Since being contacted by Watchdog, we have been working with the official UK vehicle safety agency, Vosa, to carry out tests on our entire current range of right-hand drive cars and light commercial vehicles to investigate the issues raised."