More than 60 eco-friendly vehicles embarked on a rally challenged to use the lowest amount of energy possible for the 60-mile route.
The electric, hybrid and low-emission cars, LCVs and motorcycles taking part in the inaugural RAC Brighton to London Future Car Challenge set off from Madeira Drive on the East Sussex city's seafront.
The event was intended to showcase low-emission cars of the future, with those taking part including the electric Mini E, Toyota Auris and Prius Hybrids, hydrogen-powered Honda FCX Clarity, diesel-powered VW BlueMotion Golf and Tesla electric roadster.
Taking part in the challenge were rally legends Paddy Hopkirk and David Richards, who were driving differently powered Minis. Other special entrants included former Formula One driver Perry McCarthy and Pink Floyd drummer Nick Mason.
Ahead of the rally, Professor Stephen Glaister, director of the RAC Foundation, warned that despite having the technical innovation to attempt to cut carbon emissions from cars, their development was likely to be hampered by their expense.
He said: "There is little doubt car manufacturers can overcome the technical hurdles, but what about the cost barriers?
"There is a large price difference between the most fuel-efficient models currently available and the next generation of vehicles already arriving in the showrooms.
"And there is no guarantee mass production will make these ultra-low carbon cars substantially cheaper.
"Success is unlikely to be limited by technological difficulties, but commercial pressures. The cars of tomorrow might have very low running costs, but that will be irrelevant if people haven't got the cash to buy them in the first place."
The rally was taking place a day before the annual London to Brighton Veteran Car Run, taking the traditional route in reverse.