The house flag of the Associated Portland Cement Manufactures Ltd, London.

A yellow rectangular flag, bearing a white disc in the centre with a blue border inscribed 'PORTLAND CEMENT' in blue letters and 'BLUE CIRCLE' in black letters. The flag is made of a wool and synthetic fibre bunting. It is machine sewn and the design is printed. A rope and toggle is attached.

In 1900, a group of 27 small cement manufacturers, based mostly in the Thames and Medway areas of the United Kingdom, formed the Associated Portland Cement Manufacturers Ltd (APCM). By 1909 the company acquired cement works in Mexico, and by the beginning of World War I, APCM held interests not only in Mexico but in South Africa and Canada as well. In 1911, further unification of the cement industry occurred with the merging of 33 other companies to form the British Portland Cement Manufacturers Ltd, which became a subsidiary of APCM. The two companies controlled about 80% of the cement manufacturing capacity in the UK.

APCM’s Blue Circle brand was introduced in 1928, and was used as an informal name for the company itself (the company would not officially change its name to ‘Blue Circle’ until 1978). The company continued to grow following World War II, being first listed on the New York Stock Exchange in 1953 and in 1954 opening a new cement plant in Malaysia. By this time APCM’s international operations included Australia and New Zealand in addition to Malaysia, Mexico, South Africa and Canada. APCM reached its peak manufacturing capacity in the UK in 1973, but following the energy crisis of the 1970s, the company began to slowly sell their overseas operations, mostly notably their Mexican plants to the Cemex group (now the world’s third largest cement manufacturer). In 2001, APCM (Blue Circle as of 1978) was bought by Lafarge, a French cement company which is now the world’s largest cement manufacturer.