The 220SG was the new name for the SG220 of 1928. The Cossor answer to the original screened grid valve from M-OV, the S625, was the SG210, another double ended valve. The single ended replacement for the SG210 was the SG220 that also had issues with its coated filament.
This valve dates to after 1929 when the Cossor New Process was introduced but is essentially the same electrically as the SG220.
The open Bakelite base is typical of Cossor practice of the late 1920's.
The screw top cap was replaced by the top hat style in the mid 1930's.
The balloon envelope is 44 mm in diameter, and excluding the B4 base pins is 105 mm tall.
References: Data-sheet & 1043. Type 220SG was first introduced in 1928. See also1928 adverts.