Huddersfield-based road safety charity Brake have revealed new figures today.
The current distances underestimate the time it takes for a driver to think and should be re-examined, a study commissioned by the charity concludes.
The study found it takes an average of 1.5 seconds to spot a hazard and apply the brakes, more than double the 0.67 seconds used in the Department for Transport's book.
This means the stopping distance for a car travelling at 20mph is 19 metres - seven metres more than that specified in the Highway Code.
At 40mph, it is 51 metres - 15 metres more; and at 70mph, it is 121 metres, which is 25 metres more than in the code.
Such differences should prompt the Government to increase stopping distances "as a matter of urgency", Brake said.
Spokesman Jason Wakeford said: "These figures suggest stopping distances taught to new drivers in the Highway Code fall woefully short.
"A true understanding of how long it takes to stop a car in an emergency is one of the most important lessons for new drivers.
"Understanding true average thinking time reminds all drivers how far their car will travel before they begin to brake - as well as highlighting how any distraction in the car which extends this time, like using a mobile phone, could prove fatal."
RAC spokesman Rod Dennis said the new figures should be taken seriously.
He said: "From time to time, new evidence will come to light that means it is necessary to update the Highway Code and perhaps this is one such instance.
"While the ability for cars to be able to brake more quickly has improved, our reaction times clearly haven't."
The Department for Transport said it would "carefully consider" the findings.