BSA's rugged, workaday B31 was manufactured from 1945 to the end of 1959, its overhead-valve engine providing the basis for the renowned Gold Star sports roadster. At the time of its introduction, the B31 was BSA's sole all-new model, joining the lightweight 'C' and heavyweight 'M' ranges carried over from pre-war days. Produced initially with rigid frame and telescopic front fork, the B31 gained (optional) plunger rear suspension in 1949 and an all-new swinging-arm frame in '54. A good all-round performer by the standards of its time, the B31 could cruise comfortably all day at 60mph while returning 75-plus miles per gallon, virtues that endeared it to private owners and police forces alike. Acquired for the collection in 1989, this 'rigid' B31 was first registered in Oxfordshire in April 1949 and seems to have remained in that county until at least the 1970s, as evidenced by the old-style continuation logbook on file (issued 1955). The BSA's previous registered keeper is the only one listed therein, Sidney Cain of Henley-on-Thames, who acquired it in 1955. Offered for restoration, the machine also comes with a V5C registration document. A total of 37,533 miles is displayed on the odometer.