Gibraltar

The rock of Gibraltar has a very long history, bit I will cut it very short now

Anglo-Dutch forces captured Gibraltar from Spain in 1704 during the War of the Spanish Succession on behalf of the Habsburg claim to the Spanish throne. The territory was ceded to Great Britain in perpetuity under the Treaty of Utrecht in 1713. The rock controls the entrance and exit to the Mediterranean Sea, as the Strait of Gibraltar is only 13 km.

In a referendum held in 2002, Gibraltarians rejected by a majority (99%) a proposal of shared sovereignty on which Spain and Britain were said to have reached "broad agreement". So this is still British.