Insurer Direct Line, which commissioned the research by the Transport Research Laboratory (TRL), hopes the findings will lead to support for a bill calling for a total ban on the use of hand-held mobile phones while driving.
Researchers checked the level of impairment with both hand-held and hands-free mobiles, and compared them with drivers who had exceeded the legal drink-drive limit.
The results show that drivers' reaction times were an average of 30% slower when using a hand-held mobile than when driving with excess alcohol, and nearly 50% slower than under normal driving conditions.
In the tests, drivers using mobiles were less able to maintain a constant speed and found it more difficult to keep a safe distance from the car in front.
With a hand-held phone, drivers took half a second longer than normal to react, compared to when they were drunk- equivalent to an extra 46 feet at 70mph before reacting to a hazard on the road. Also, drivers using either hands-free or hand-held mobiles missed more road warning signs than when drunk.
Janet Anderson, MP for Rossendale and Darwen, is introducing a Bill to make the use of a hand-held mobile phone while driving an offence.
Drivers using mobiles can currently be prosecuted for driving without due care if the use of the phone results in their driving standard suffering, with a maximum fine of £2,500, licence endorsements of between three and nine points and discretionary disqualification.
Dominic Burch, Direct Line's road safety campaign manager, said: 'Eventually we would like to see the use of mobile phones when driving, both hands-held and hands-free, become as socially unacceptable as drink-driving.'