Researchers from the University of Sussex have found that using a hands-free phone whilst driving is just as distracting as holding the phone in your hand, BBC News reports.
According to the scientists, the part of the brain that is used to watch the road can be used by drivers to visually imagine what they are talking about when having a conversation.
The researchers' study consisted of 20 male and 40 female volunteers taking part in video tests, while sitting behind a steering wheel in a car seat.
The volunteers were then separated into groups, with one group allowed to "drive" undistracted while the other two groups heard a male voice from a loudspeaker 3ft (0.9m) away.
The research found that those "drivers" that were distracted by the voice conversing with them took just under a second longer to respond to events.
These events included a pedestrian stepping off the pavement, an unexpected vehicle parked at a junction and an oncoming car driving on the wrong side of the road.
The study's lead author has said the findings make a case for all phones to be banned from cars.
Currently, it is illegal to a ride a motorcycle or drive using hand-held phones or similar devices in the UK. If caught, drivers get an automatic fixed penalty, three penalty points and a fine of £100.
While drivers can use hands-free phones, sat navs and two-way radios, they can be penalised if police think they are distracted and not in control of the vehicle.
Do you use hands-free when driving?