Driven by Vauxhall's archivist and resident eco-driving expert Andrew Duerden, with co-driver Neil McIntee, Editor of VansA2Z.com, the 2.0CDTi-powed new Vauxhall Vivaro ecoFLEX registered 65.16mpg against a combined figure of 40.90mpg.
This s result was reportedly the best percentage improvement for a commercial vehicle as well as overall including cars as well as vans.
The Fleet World MPG Marathon is the UK longest-running economy driving event. The two-day event took place in the Cotswolds with separate routes covering 350 miles of countryside including a mixture of A and B roads and motorway driving.
Duerden said: "Neil and I are, as they say, over the moon to win the overall best percentage improvement in the Vivaro ecoFLEX.
"Fuel economy is a top priority for Vauxhall customers looking to reduce running costs and our MPG Marathon win proves what a frugal van the Luton-built Vivaro is."
Launched earlier this year, the revised new Vauxhall Vivaro ecoFLEX features a range of green technology features including exhaust gas recirculation cooling and optimised gear ratios. There's also improved thermal management, low rolling resistance tyres and an aerodynamic kit.
Vauxhall's MPG Marathon win follows its topping the van sales charts to private buyers and small businesses in the crucial plate change month of September.
Building over 70,000 vehicles alone last year at its plants in Luton and Ellesmere Port, Vauxhall is the UK's largest manufacturer of commercial vehicles.