E G Bates 20 3/4" frame

"Bates is one of the most highly regarded of the English lightweight frame builders. The company became famous for its racing successes of the 1930s, 1940s and 1950s but it is probably best known for the unique 'Cantiflex' frame tubing and odd-shaped 'Diadrant' front forks used for many of their racing and club machines."

http://www.classiclightweights.co.uk/builders/bates.html