Dewis was the test driver who, on 20 October 1953 at Jabbeke, Belgium, drove a Jaguar XK120 to 172.412 mph, a record for production cars.

The car had several aerodynamic modifications, including a distinctive bubble-shaped, air-tight canopy from a glider aircraft.

Despite a damaged tyre, and against the instructions of Jaguar Director, Lofty England, the car was driven by Dewis at high speed.

In June 2016 he appeared on the BBC's Top Gear TV show with the Jaguar F-type SVR.

In the 2015 New Year Honours Dewis was invested as an Officer of the Most Excellent Order of the British Empire (OBE) for services to the Motor Industry.