London Thamesport is a container seaport on the River Medway, serving the North Sea. It is on the Isle of Grain, in the Medway unitary authority, Kent, England in the United Kingdom. It is sited on the former Port Victoria.

In 1953, the Anglo-Persian Oil Company (later British Petroleum) developed a large oil refinery, Kent Oil Refinery, in the south of the Isle of Grain. A fuel depot with an attached port had existed there since 1928. But from 1953, over ten million tons of crude oil were processed annually on the 4 km² site. This led to the establishment of the oil-fired power station at Grain and dual-fuel capable Kingsnorth. In practice, Kingsnorth uses coal. The refinery was closed on 27 August 1982, and work was transferred to other BP locations. The plant was taken over by British Gas plc (at that time still nationalised), which used a small part of the site for the storage of liquefied natural gas. Three quarters of the site remained unused.

In 1987 British Gas submitted plans to use 0.87 km² of the disused refinery site as a Container port. Building began in 1989. The risk capital financing of the £150 million project, named Thamesport, took place through the operating company Thames Estuary Terminals Ltd., later Thamesport Ltd. By March 1990 the enterprise had a capacity of approximately 360,000 TEU per year.