Gibraltar, which gave access to both the Atlantic Ocean and the Mediterranean Sea, was already a well established naval base. In the 17th Century the British briefly had a colony in Tangier (1661-84), and expressed interest in Ceuta in North Africa which came under Spanish control.
Malta was also acquired by the British is 1813 and the British Military remained there until 1979.
Corfu was a British Protectorate from 1815 to 1863 during which time various fortifications were built.
Cyprus was also a British Protectorate between 1878 and 1914 and eventually became a Crown Colony.
With the opening of the Suez Canal in 1869 the Mediterranean assumed even more importance as a conduit to British India.
Alexandria and parts of Egypt which became a quasi protectorate between 1882 and 1913. Numerous RML batteries were established in and around Alexandria, but they remained under Egyptian control.
Menorca was in British possession between 1708 and 1802, although briefly expelled by the Spanish in 1781 and French in 1763. A naval dockyard was built at Mahon.