The house flag of United Towing Ltd, Hull. A blue pennant with a five-pointed white star bearing a blue letter 'U'. The flag is made of a wool and synthetic fibre bunting. It has a cotton hoist and is machine sewn. A rope and Inglefield clips is attached.

In 1920, seven Humber tug companies joined forces to form United Towing, with a fleet of 36 vessels. The managing director, Thomas Clarkson Spink, was appointed to a post he was to keep for the next 40 years. Initially the company concentrated on port, river, and coastal towage, towing coal barges, meeting the sail grain ships from Australia, and taking barges across the North Sea. Tasks also included fire fighting, restoring anchors and cable to the local trawlers and hauling off stranded vessels.

From 1925 company operations spread worldwide towing ships, barges, dredgers and dry-docks. Modernisation of the company began in 1959, but was speeded up by the purchase of United Towing by the Boston Deep Sea Fishing Group in 1962. The size of the tugs increased due to the demands of modern shipping, specifically the super tanker and the off shore rigs. New vessels such as the replacement 'Seaman', a multipurpose tug and 'Salvageman', the most powerful tug in the fleet were put into service. However by the early 1980s the increased competition from offshore support vessels and the decline in the general towage and salvage business led to the downsizing of the fleet to just three vessels.

In 1987 a majority interest in United Towing's parent company, North British Maritime Group Ltd, were bought by Howard Smith Ltd of Australia. In 1989 the remaining shares were bought making United Towing a wholly owned subsidiary of the Australian company. The company then changed policy and withdrew from ownership of the large ocean going tugs, concentrated on the management of such vessels and maintained its salvage operations. Apart from commercial towing, the ships played a service role throughout the Second World War and the Icelandic cod wars when they provided protection for the trawler fleets; they later served in the Falkland conflict. The headquarters of Howard Smith (UK) Ltd, incorporating United Towing, is still in Hull.