On 2 April 1982, Argentine forces launched an invasion of the Falkland Islands, a British overseas territory in the South Atlantic, beginning a 10-week undeclared war. The military action was ordered by the ruling junta in Argentina, led by General Leopoldo Galtieri, which sought to assert its long-standing claim to the islands, known in Argentina as Las Malvinas.

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The invasion began in the early hours of the morning, with Argentine commandos landing near the capital, Stanley. The British governor, Rex Hunt, was forced to surrender later that day. The following day, Argentina also invaded the island of South Georgia. Argentina had already established an unauthorised presence in the South Sandwich Islands in 1976.

Margaret Thatcher’s government was accused of failing to foresee and deter the attack.

On 3 April, both Houses of Parliament were recalled for the first time on a weekend since the Suez crisis in 1956 to be updated on the government’s response.

Lord Carrington, the foreign secretary, addressed peers in the upper chamber.

Opening the landmark commons debate, Thatcher told MPs that, “for the first time for many years, British sovereign territory has been invaded by a foreign power.”

The prime minister stated: “After several days of rising tension in our relations with Argentina, that country’s armed forces attacked the Falkland Islands yesterday and established military control of the islands.”

She characterised the invasion as an act of “unprovoked aggression” with “not a shred of justification.”

Thatcher announced that a “large task force” would be dispatched to the South Atlantic to recapture the islands. HMS “Invincible”, the prime minister said, would lead the naval task force and leave port on Monday (5 April).

She declared: “The people of the Falkland Islands, like the people of the United Kingdom, are an island race. Their way of life is British; their allegiance is to the Crown. They are few in number, but they have the right to live in peace, to choose their own way of life and to determine their own allegiance.”

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Michael Foot, the Labour leader of the opposition, said that the people of the Falkland Islands had been “betrayed”.

He added: “The responsibility for the betrayal rests with the government.”

Opposition MPs demanded the resignation of the defence secretary, John Nott, who was blamed for leaving the Falklands vulnerable to the Argentine invasion.

Nott, in his contribution to the debate, defended his actions. “If we were unprepared, how is it that from next Monday, at only a few days’ notice, the Royal Navy will put to sea in wartime order and with wartime stocks and weapons?”, he asked.

“That force will include the carriers HMS ‘Invincible’ and HMS ‘Hermes’, the assault ship HMS ‘Fearless’ and a number of destroyers and frigates armed with anti-surface and anti-air missiles.”

Nott added: “I conclude by saying – [MPs collectively: ‘Resign’] – that the government do not pretend that the situation is anything but extremely grave. The resolution of this problem will undoubtedly be all the more difficult since the occupation.

“We intend to solve the problem and we shall try to solve it… by diplomatic means, but if that fails, and it will probably do so, we shall have no choice but to press forward with our plans, retaining secrecy where necessary and flexibility to act as circumstances demand.”

The commons debate is said to have convinced Carrington to resign as foreign secretary. It has been suggested that Carrington’s departure reflected a recognition of fact that, at a time of crisis, the foreign secretary should be a member of the House of Commons and therefore answerable to MPs.

In his letter of resignation, Carrington recognised that the invasion of the Falkland Islands “led to strong criticism in parliament and in the press of the government’s policy.”

He added: “In my view, much of the criticism is unfounded. But I have been responsible for the conduct of that policy and I think it right that I should resign.”

The outgoing foreign secretary called on the government to do “everything we can to uphold the right of the Islanders to live in peace, to choose their own way of life and to determine their own allegiance.”

In her response, Thatcher said she did her “utmost throughout Saturday and Sunday to dissuade” Carrington from resigning. The prime minister accepted Carrington’s resignation with the “greatest reluctance”.

Richard Luce, the minister of state for foreign affairs, and Humphrey Atkins also resigned. Atkins had served as the chief government spokesman in the House of Commons for foreign and commonwealth affairs.

Luce said the “Argentinian invasion of the Falkland Islands has been a humiliating setback to the people of the Islands and to the United Kingdom.”

Francis Pym, previously the leader of the House of Commons, was chosen to succeed Carrington.

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The 74-day war that followed claimed the lives of 649 Argentine and 255 British servicemen, as well as three Falkland Islanders. The war ended on 14 June when the commander of the Argentine garrison at Port Stanley surrendered to British troops.

Britain’s decisive victory helped forge Thatcher’s reputation as the “Iron Lady”, and proved a significant factor in the Conservative Party’s landslide victory at the 1983 general election.

The Conservative Party’s 1983 manifesto stated: “In a troubled world, Britain is increasingly respected because we stand up for our own interests. But we are also respected because we stand up for the cause of freedom and the spread of prosperity throughout the world.

“We resisted unprovoked aggression in the Falkland Islands, when the loyal support of our friends throughout the world reminded us of our common heritage of freedom. We will continue to uphold the principles for which we fought.”

Thatcher was previously regarded as one of the most unpopular prime ministers in history, having overseen rising unemployment and recession in her battle against inflation during her first years in office. The prime minister, in short, had an exceptionally good war.

Thatcher’s authority to see out her hitherto unpopular economic programme was secured, in effect, by overseas developments.

The Tories won a landslide majority of 144 seats – the largest since Labour’s victory in 1945 – at the 1983 general election. Labour won 209 seats (down 60 on the 1979 general election). It marked the party’s worst election performance since 1918.

Pym was sacked as foreign secretary following the 1983 general election. It came after he suggested that “landslides don’t on the whole produce successful governments”.