The house flag of Clan Line Steamers Ltd (Cayzer, Irvine & Co., Ltd), London and Glasgow. A rectangular red flag bearing a white diamond with a red rampant diamond in the centre. The flag is made of a wool and synthetic fibre bunting with a linen hoist. It is machine sewn and the design is printed. A rope and two Inglefield clips is attached.

The shipping line was founded in 1878 by Charles Cayzer to run direct passenger steam services between Bombay and the UK via the Suez Canal as Cayzer, Irvine & Co., Liverpool. The company vessels all had names with the prefix 'Clan'. Services were extended to South Africa in 1881 and in the same year the company opened a larger office in Glasgow. Clan Line Steamers Ltd was launched in 1890 and the company extended its routes in the Persian Gulf and to North America - it was by now also carrying cargo. Cayzer Irvine & Co. was incorporated in 1907 but remained in the hands of the Cayzer family.

After the death of Charles Cayzer in 1916, the business was continued by his sons. By the late 1930s it was the biggest cargo carrying concern in the world. The fleet inevitably sustained losses in both world wars. The Thompson Steam Shipping Co. was acquired in 1952. The company changed over to motor ships in the 1950s. With the advent of containerisation, the company ran down the shipping side of the business in the early 1980s, having diversified into other business ventures. 'Clan Macgregor' made the final Clan Line voyage in 1981.