On 17 April 1969, the Representation of the People Act, a landmark piece of legislation that lowered the voting age in the United Kingdom from 21 to 18, received royal assent.

The act, sometimes referred to as the Sixth Reform Act, made Britain the first major democratic state to enfranchise citizens at 18.

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The reform was the culmination of a growing consensus that the “age of majority”, the legal threshold at which a person is considered an adult, should be lowered to reflect societal changes. But it followed a convoluted political pathway.

The process was advanced by the Latey committee, appointed by the Labour government in July 1965, which considered the age of majority (21 at this time). It scrutinised marriage, wardship, contracts and property. The voting age, however, lay beyond the committee’s terms of reference, as prescribed by the government.

Reporting in July 1967, the committee found that the “young people today, as the old never tire of remarking, are not what they were.”

The report added: “They are largely literate and educated; they are far better off financially and far more independent of their parents; they are taught to think and enquire for themselves and mostly do so; and their experience of life is wider…

“This committee is convinced that we must ensure that the young go out into the world as fully prepared for their adult responsibilities as possible, and that in giving them adult status at 18 we are doing no more than recognising the simple facts.”

In a debate of the report in the commons, Michael Stewart, the first secretary of state, noted that the Latey committee “deliberately refrained [from] discussion of the voting age”.

But he added: “If, after consideration of the various matters raised in the Latey report, the House or country came to the view that young people are fit to marry without their parents’ consent, to enter into valid contracts, and to do all the other things recommended in the report at the age of 18, it might well be that this was bound to influence the judgment of the House and the public about the voting age.”

With the government having accepted the Latey committee’s recommendations, Richard Crossman, the then leader of the House of Commons, came to the conclusion that voting reform was now inevitable. He wrote in his diary that “it was obvious that if you reduced the age for everything else it was impossible to keep voting at 20 so… we now had to recommend votes at 18”.

The Family Law Reform Act was passed in 1969, as per the Latey committee proposals.

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Meanwhile, the issue of the voting age was referred to a speaker’s conference in May 1965. A previous speaker’s conference in 1944 had rejected any lowering of the voting age.

The conference, interrupted by the 1966 general election and the death of a speaker (Sir Harry Hylton-Foster), recommended reducing the age only to 20. This position was agreed by 24 votes to one. A resolution, supported by the Labour Party, to reduce the age to 18 was rejected 22 votes to three.

The Labour Party’s general election manifesto for the 1966 election stated: “The Labour Party has proposed to the speaker’s conference the introduction of Votes at [18], to add a necessary political dimension to the increasingly important economic and social position of young people”.

Labour won a landslide 98-seat majority at the 1966 election.

In a July 1968 statement responding to the speaker’s conference report, James Callaghan, the home secretary, cautiously insisted the government would overrule its findings on the voting age issue.

Callaghan told MPs: “The government have already announced their acceptance of the recommendation of the Latey committee that the age of majority should in future be 18, and the government accordingly recommend in the [newly published] white paper that the minimum age for voting should also be reduced to 18 years.”

The parliamentary Labour party (PLP) and the Wilson cabinet had approved ‘Votes-at-18’ on 9 May and 30 May 1968 respectively.

The white paper to which Callaghan referred (published July 1968) formed the basis of the Representation of the People Act 1969. The document was also based on the conclusions of a separate ‘electoral advisory conference’, composed of government departments, registration officers and representatives of the political parties.

The Representation of the People Bill received its commons second reading on 18 November 1968. Leading the debate for the government, Callaghan said: “18 is the age which Latey found to be suitable for the assumption of civic responsibilities. It is an age which appeals to the government as being appropriate for the casting of a vote.”

At committee stage, an amendment in the name of George Strauss, a Labour MP who had been a member of the speaker’s conference, was moved to lower the age, not to 18, but to 20. It was rejected by 275 votes to 121.

During the bills Lords stages, where votes-at-18 met some resistance, Conservative Peer Lord Brooke argued the government had been “absolutely hypnotised by the majority report of the Latey committee.”

Of the bill’s convoluted genesis, academics Thomas Loughran, Andrew Mycock and Jonathan Tonge have noted: “Latey was supposed to be arbiter of adulthood and the speaker’s conference the determinant of the age of franchise. However, the Labour government simply coupled what it had initially decoupled – thus Latey trumped the speaker’s conference.”

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As well as lowering the voting age, the act also abolished the remaining plural voting rights for university graduates and business owners, ensuring the principle of ‘one person, one vote’ was established for parliamentary and local government elections.

The Representation of the People Act 1969 marks the last major extension of the UK electoral franchise. 18-year-olds voted for the first time in the general election of June 1970.

In January 1985, Liberal MP Jim Wallace proposed a bill under the 10-minute rule, which called for the creation of a framework “within which young people can participate more fully in the affairs of their community and the decisions that affect or shape their lives”.

He called for the voting age to be lowered further, arguing that young people “have an important stake in the future, and what they lack in experience may be more than compensated for by the fresh ideas that they can bring forward.”

Wallace added: “A number of causes now coming to the fore in politics – for example, environmental concern – were espoused by young people long before they gained political respectability.”

In 1999, Liberal Democrat MP Simon Hughes proposed an amendment to the Representation of the People Bill to lower the voting age to 16. Hughes argued that lowering the age would “engage many people who feel alienated” and help “deal with apathy in this country.”

The minister on duty, Mike O’Brien, spoke against the amendment. He stated that “there is more likely to be a higher percentage of people aged 18 who are able to exercise judgment properly with maturity and independence than of those aged 16.”

O’Brien added: “18 is the most common voting age throughout the world, and we believe that it is still the most appropriate minimum age.”

The amendment was defeated by 434 votes to 36 – a majority of 398. It was supported by Liberal Democrat MPs, including future leaders Charles Kennedy and Menzies Campbell, as well as a handful of Labour MPs, notably Tony Benn, Jeremy Corbyn and John McDonnell.

In January 2003, the Votes at 16 Coalition was founded to campaign for the extension of the franchise to 16- and 17-year-olds. This alliance grew to include organisations such as the Electoral Reform Society and the National Union of Students.