The WW II Flying Flea and the 126cc, 1946-1953 Model RE that it turned into all had a ridged rear frame with no rear suspension at all (if you don't include the seat).
1953 was the first year for the "Ensign", and it did have that double spring system for the rear suspension so this bike must be a 1953 or later model.
Although it can be dangerous to go by photos in books, the 1955 Ensign was the first year the springs on the rear were enclosed like the one in the OP.