Gibraltar is a colony. Since the 1960s, it has been on the United Nations list of "Non-Self-Governing Territories awaiting decolonisation". This colonial vestige is incompatible with resolution 1514 (XV) of 1960 on decolonisation. The United Nations has pointed out that, in the decolonisation process of Gibraltar, the applicable principle is not that of self-determination of peoples but rather that of restitution of Spanish territorial integrity. Spain has repeatedly asked the United Kingdom to enter into negotiations, in compliance with the provisions of the United Nations since 1965, to reach a definitive solution to this dispute.
Gibraltar was ceded to the United Kingdom by the Treaty of Utrecht. However, only "the city and castle of Gibraltar together with its port, defences and fortresses belonging to it" were ceded. The isthmus, like the adjacent waters or the overlying airspace, was not ceded by Spain and has always remained under Spanish sovereignty. The continued de facto occupation by the British does not meet the requirements of international law for the acquisition of sovereignty. That is why Spain has always stressed that the occupation of the isthmus is illegal and contrary to international law and, therefore, has always demanded its unconditional return. Spain does not recognise the occupation of the isthmus or the fence as a border.
The main documents relating to the Gibraltar dispute are as follows:
- The Treaty of Utrecht. Signed on 13 July 1713, Article X cedes to the British Crown "the full and entire ownership of the city and castle of Gibraltar, together with its port, defences and fortresses belonging thereto".
- Resolution 2070 of the XX General Assembly of the United Nations. Adopted on 16 December 1965, it invites for the first time the Governments of Spain and the United Kingdom to begin talks on the sovereignty of Gibraltar without delay.
- Resolution 2353 of the XXII General Assembly of the United Nations. Adopted on 19 December 1967, it establishes that any colonial situation that destroys, in whole or in part, the national unity and territorial integrity of a country is incompatible with the purposes and principles of the Charter of the United Nations and specifically with paragraph 6 of General Assembly resolution 1514 (XV) on general decolonisation.
- Resolution 2429 of the XXIII General Assembly of the United Nations. Adopted on 18 December 1968, it called on the United Kingdom to put an end to the colonial status of Gibraltar by 1 October 1969.
- The Lisbon Declaration. Signed on 10 April 1980, it reflects the commitment of the two Governments to resolve the problem of Gibraltar in a spirit of friendship and in accordance with the relevant United Nations resolutions.
- The Brussels Declaration. Signed on 27 November 1984, it lays the groundwork for a new negotiating process that includes sovereignty issues.
Spain has on multiple occasions invited the United Kingdom to resume, as soon as possible, bilateral negotiations on sovereignty issues.
Since European Union law applied on the Rock because of the United Kingdom's membership of the Union, the United Kingdom's exit necessarily implies the exit of Gibraltar. To ensure that this exit was in line with Spanish interests, Spain entered into negotiations with the United Kingdom on the withdrawal from Gibraltar which have resulted in a Protocol on Gibraltar annexed to the Withdrawal Agreement, four bilateral memorandums of understanding (on citizens' rights, environmental cooperation, tobacco, and police and customs cooperation), signed on 29 November 2018 and an international agreement with the United Kingdom on tax matters signed on 4 March 2019.
Once Brexit has been consummated, an agreement is being negotiated that regulates the relationship between the European Union and the United Kingdom in relation to Gibraltar and that develops the different contents of the so-called New Year's Eve Agreement of 2020 covering a wide list of matters in which the EU is competent. This agreement will require the prior consent of Spain.