The nickle plating made me wonder, but after looking at pictures, it looks to be a Norton "feather bed" frame. From an article in Classic Bike magazine about how it got it's name:
"At the Isle of Man TT, the first round of the 1950 world championships, Norton took the first three places, with Irish ace Artie Bell ahead of young rising star Geoff Duke and TT veteran Harold Daniell. At the prize-giving, Daniell said the new chassis was so comfortable he could have fallen asleep: "It was like a feather bed"."