On 10 September 1967, the people of Gibraltar voted by a near-unanimous margin to retain their link with Britain and reject Spanish sovereignty.

In the end, 12,138 votes (99.19%) were cast in favour of remaining British, with only 44 votes (0.36%) supporting a transfer to Spanish rule. The referendum was held on a turnout of 96.57%.

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The vote was called by Harold Wilson’s Labour government in response to mounting diplomatic pressure from Spain, then ruled by the dictator General Francisco Franco.

The Franco government seized on the United Nations decolonisation process to demand the return of the territory. Spain had imposed restrictions at the border and campaigned internationally on the issue.

A UN Resolution adopted on 20 December 1966 asked “the administering power [Britain] to expedite, without any hindrance and in consultation with the government of Spain, the decolonisation of Gibraltar”.

Franco called for the cancellation of the Treaty of Utrecht of 1713, which ceded Gibraltar to Britain. Wilson resolved that a referendum would demonstrate Gibraltar’s will to remain British.

The referendum policy was announced to the House of Commons on 14 June 1967 by Foreign Office minister Judith Hart.

Hart referred to Britain’s competing obligations to the 1966 UN resolution, Article 73 of the UN charter and the Treaty of Utrecht.

But she said that “Britain could never agree that decolonisation would mean the incorporation of Gibraltar into Spain against the wishes of its people.”

Hart therefore declared: “I must repeat Her Majesty’s Government’s firm belief that decolonisation cannot consist in the transfer of one population, however small, to the rule of another country, without regard to their own opinions and interests.

“We therefore think that the next step… should be to give the people of Gibraltar an opportunity to express their views, by a formal and deliberate act, on what would best serve their interests.”

Hart set out the two options, ‘A’ and ‘B’, that would be included on the bilingual ballot papers.

Option A was “To pass under Spanish sovereignty in accordance with the terms proposed by the Spanish Government to the Government of the United Kingdom on 18th May, 1966”.

And option B read: “Voluntarily to retain their link with the United Kingdom with democratic local institutions and with the United Kingdom retaining its present responsibilities.”

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On 1 September, the UN special committee on colonialism declared that the vote would violate the United Nations Charter. It suggested that the current residents of Gibraltar were not entitled to self-determination because they were not indigenous to the territory.

Nevertheless, the referendum result was an effectively unanimous rejection of the Spanish claim.

Gibraltar’s chief minister, Joshua Hassan, said the referendum was “the first opportunity for Gibraltarians to express in a free and democratic way where their interests lie.”

In retaliation, the Franco regime intensified its blockade. This led to the complete closure of the land frontier in June 1969, severing communication and stranding residents. The border was not fully reopened until 1985 as part of Spain’s negotiations to join the EU.

In the immediate aftermath of the referendum, the British government passed the Gibraltar Constitution Order 1969. The preamble to this constitution enshrined the UK’s commitment to the result.

It stated: “Whereas Gibraltar is part of Her Majesty’s dominions and Her Majesty’s Government have given assurances to the people of Gibraltar that Gibraltar will remain part of Her Majesty’s dominions unless and until an Act of Parliament otherwise provides, and furthermore that Her Majesty’s Government will never enter into arrangements under which the people of Gibraltar would pass under the sovereignty of another state against their freely and democratically expressed wishes.”

The date of the 1967 referendum, 10 September, is now celebrated annually as Gibraltar National Day.

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Gibraltarians reaffirmed their link with the UK in a second referendum in 2002, when a proposal for joint Anglo-Spanish sovereignty was rejected by a similarly overwhelming margin.

The 2002 referendum came about after the UK foreign secretary, Jack Straw, entered into negotiations with Spain about the future of Gibraltar.

In a statement to the House of Commons on 12 July 2002, Straw declared that “Britain and Spain should share sovereignty over Gibraltar”.

This was met with furious opposition from MPs, who shouted Straw down with cries of “Surrender!” and “Sell out!”.

Straw contended that the “status quo was damaging to Gibraltar, and also damaging to Britain”.

He argued the sovereignty dispute was damaging to Gibraltarians who have to “put up with everyday disruption: queues at the border, insufficient telephone lines, inadequate air services and much else”.

The dispute was also “damaging to Britain’s interests”, Straw said, because Spain “has repeatedly blocked European measures we want”.

Straw added: “We had hoped to reach agreement with Spain by the summer, but I have also made clear many times that no deal is better than a bad deal. There have been distinct red lines throughout this process.”

Michael Ancram, the shadow foreign secretary, condemned the statement as a “disgrace and a sell out”.

He added: “Does he not understand that this issue is not about our relations with Spain? It is about the democratic rights of the people of Gibraltar… Does he not understand that his broad agreement to share sovereignty is a betrayal of the people of Gibraltar?”

Gerald Kaufman, the veteran Labour MP, insisted that “Labour members will not go along with what he is doing and that just as this House… would not accept the sell out of the Falklands by the Tory government, so we shall not accept the sell out of Gibraltar by a Labour government”.

Michael Fabricant, a Conservative MP, accused Straw of conducting “a policy of flying one flag…the white flag”.

The only voice of support, though it was heavily qualified, came from Liberal Democrat foreign affairs spokesperson Menzies Campbell.

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The government of Gibraltar strongly opposed Straw’s announcement, and went ahead with a referendum before any treaty could be agreed between Britain and Spain.

Straw referred to the proposed referendum as “eccentric” and said the UK government would not recognise it.

The foreign secretary said: “My concern about this is that the day after the referendum result the people of Gibraltar are going to wake up and they’ll still be faced with the same reality as they had been the day before.”

Peter Caruana, Gibraltar’s chief minister, said: “Only the Foreign Office could describe a referendum which is an opportunity for ordinary people to express their views in private and in confidence as an undemocratic and short-changing step.”

Ancram and the Conservative Party backed the referendum.

The referendum question was as follows: “On 12 July 2002 the Foreign Secretary, Jack Straw, in a formal statement in the House of Commons, said that after twelve months of negotiation the British Government and Spain are in broad agreement on many of the principles that should underpin a lasting settlement of Spain’s sovereignty claim, which included the principle that Britain and Spain should share sovereignty over Gibraltar. Do you approve of the principle that Britain and Spain should share sovereignty over Gibraltar?”

98.97% of Gibraltarians said no, versus 187 (1%) who voted ‘Yes’.

Responding to the result, Caruana said: “We say to the British government: take stock of this referendum result, it’s the will of the people of Gibraltar.”

He described the route to joint sovereignty as “a dead end road for everyone, including the British Government”.

Straw’s conduct and handling of negotiations with Spain was criticised in a report by the foreign affairs committee of MPs.

The report stated: “We reject the foreign secretary’s view that it is ‘eccentric’ for the government of Gibraltar to hold its own referendum. We consider that in British Overseas Territories it is of great importance that democratic expressions of view should take place when territories themselves so determine.

“We recommend that the British government take full account of the views of the people of Gibraltar as expressed in the referendum held on 7 November.”

It added: The government was wrong to negotiate joint sovereignty, when it must have known that there was no prospect that any agreement on the future of Gibraltar which included joint sovereignty could be made acceptable to the people of Gibraltar, and when the outcome is likely to be the worst of all worlds – the dashing of raised expectations in Spain, and a complete loss of trust in the British government by the people of Gibraltar.”

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After the 2002 referendum, the British and Gibraltar governments negotiated a new constitution. The Gibraltar Constitution Order 2006 reduced the powers of the governor of Gibraltar, a post appointed by Britain, transferring them to elected officials.

The order, which also enshrined a bill of “fundamental rights and freedoms” into the constitution, was approved by 60.42% of Gibraltarians in a 2006 referendum.

In 2016, Gibraltarians voted overwhelmingly for the United Kingdom to stay in the European Union (EU), with 95.91% supporting the ‘Remain’ position.

823 Gibraltians (4.1%) voted for the United Kingdom to leave the EU.