There were British imports with no backmarks but the one you posted ain't one of them. The construction on yours is of a later period. In the first 2 years of the CW, British manufacturers would ship Southern buttons with their name one the back. After CS blockade runners were captured with their cargo which had British manufacturer names on them, they went to no backmark or Superior Quality and other generic backmarks.
Was watching this on ebay, thanks for the insight. ucvrelics, why were the British companies taking their names off the back? Afraid of retribution from the Yanks??