The relationship, largely driven by the nations' common interests as maritime countries on the edge of Europe and close to larger continental neighbours, dates back to the Middle Ages in 1373 with the Anglo-Portuguese Alliance.

Her dowry gave Britain Tangiers and Bombay, plus free trade to Portuguese colonies in Brazil and Asia.

In the later half of the century, as Portugal's imperial power declined following Brazil's independence, there were disputes between itself and the United Kingdom in southern Africa (1890 British Ultimatum) which was a great embarrassment for the Portuguese monarchy and colonial prestige.

While officially neutral in World War II, Portugal remained friendly to the British, a counterpart to Spain's cooperation with the Axis.

[12] In World War II, Prime Minister António de Oliveira Salazar was committed to the six-century-old treaty (which had been renewed in 1899).

Lisbon was the base for International Red Cross operations aiding Allied POWs, and a main air transit point between Britain and the U.S.[13] The states are members of NATO and Organization for Security and Co-operation in Europe.

In 1557 and 1842, and in 1898, Britain and Portugal established Hong Kong and Macau on both sides of the Pearl River Estuary along the coast of Guangdong Province.

Today, Hong Kong and Macau have been established a Chinese Special Administrative Regions on 1 July 1997 and 20 December 1999, and ended the rule of 156 and 442 years, respectively, for British and Portuguese.