The  Significant Six

 

 Year

Marque

Model

Engine

  
1925 Royal Enfield Standard 350
1926 Ariel Model D (Touring) 500
1927 Royal Enfield Sports 351 350
1930 Ariel Model G 500
1937 Ariel Red Hunter 350
1947 Matchless G80 500

and here are the ones that got away...
1919 Triumph Junior 225
1925 AJS E1 800
1926 Douglas EW 350
1931 Norton Model 18 500
1936 Velocette MAC 350
1936 Brough Superior SS80 1000
1957 Norton Model 77 600
See the Jaguar