This year's MPG Marathon event is set to see its youngest-ever competitors - but these are no ordinary 17-year-olds.

Rory Carmichael and Eloise Peabody-Rolf, who will compete as a team in the "lean-driving" event, may have only passed their driving tests recently, but they have both been driving since the age of 11 as part of The Under-17 Car Club.

In that time they have driven an astonishing 300 vehicles, including an Aston Martin and a 44-tonne articulated lorry.

The teenagers will be competing in a Honda Civic i-DTEC, which has official efficiency figures of 78.5mpg and 94g/km. An identical car won the event last year.

What's more, the pair will go head-to-head with their driving instructors, BBC transport correspondent for southern England Paul Clifton, and Shaun Cronin, the man responsible for the roads policing team in Dorset. They will be using a Honda CR-V with the same engine as the Civic.

"Rory and I are very excited to be competing in the MPG Challenge, and greatly appreciate the fantastic opportunity Honda is giving us," said Eloise, who is currently studying for A-levels at Portsmouth Grammar School and will be the main driver.

"It will certainly be a new experience as neither of us have ever competed in such an event before, let alone tried 'economy driving'."

Paul Clifton said that Eloise and Rory faced an exciting challenge. "The Car Club and Honda UK would very much like to demonstrate that youth is no bar to good, safe, economical driving; what matters is the right training and, above all, the right attitude behind the wheel," he said.

"Eloise and Rory will be up against some of the best professional drivers in the country; proven experts at ultra-economical driving. They are in a standard Honda Civic 1.6 diesel, which neither has driven before. Two weeks before the event, Eloise had not even driven on a motorway."

This year's 300-mile challenge runs across September 29-30, with the participant that uses least fuel over that time declared the winner.