The house flag of Brocklebank Line. A rectangular flag divided vertically into white and blue. The design was in use by the company as early as 1820 and was flown from the fore on the orders of the owner, Thomas Brocklebank. Flag A in the present day International Code is swallow-tailed because of the refusal of Brocklebanks to change their house flag. The flag is made of a wool and synthetic fibre bunting. It has a cotton hoist and is machine sewn. A rope and toggle is attached.

The business was founded by Daniel Brocklebank, who after an early career as a New England shipbuilder and British merchant retired to shore as a ship owner and shipbuilder, based in Whitehaven. In 1800 he passed the business on to his sons Thomas and John, (the firm was re-named Thomas & John Brocklebank in 1801). It originally traded with the Americas, but after the ending of the East India Company's monopoly of trade with India, the company opened routes to the subcontinent in 1815 and later to the Far East, starting services to China in 1860. In 1819 Thomas Brocklebank opened an office in Liverpool which city became the company's main base.

The company acquired its first steamer in 1889, but operated sailing ships until 1906. By this time the firm were mainly ship owners. In 1919 Cunard acquired the majority holding of Brocklebank shares, the rest was held by Anchor Lines; however the composition of the board remained unchanged. The company sustained heavy losses in the First and Second World Wars and was hit by the trade restrictions that followed the independence of India and Pakistan in 1947. The temporary closure of the Suez Canal and containerisation led to the end of trade to India. Cunard sold the two last liveried Brocklebank ships in 1983 and this marked the end of the company as a separate entity.