The aircraft was being leased by Imperial from British Airways.  The flight was enroute from London to Zurich with a stop in Basel.  One of the engines had been giving trouble at 10,000 feet and the aircraft was descending.  At 3,000 feet the carburetor caught fire, possibly caused by a lightening strike, and although the pilot followed the recommended course, by opening the throttle and diving, the flames spread.  The Captain put the aircraft down in a field near Saint Sauveur, at an approximate speed of 120 mph.  The undercarriage broke but the aircraft did not turn over.  Captain Prowse and First Officer Whincop, slightly burned by the flames near the cockpit, jumped out and opened the cabin door to let the nine passengers escape.  The aircraft was burned out.  The passengers continued their journey by car. According to an item in The Times of London of 12 August, "The machine and the mails it was carrying were destroyed".  Part of the mail was in fact salvaged in burned condition.  Various cachets and labels were applied by different destination post offices in Switzerland.