All this now seems a terribly long time ago. More than a few half-lives have passed since anti-nuclear fervour shook New Zealand, but Leadbeater is convinced the passions which caused a ruckus in Queen St 29 years ago were instrumental in forcing the Lange Government to act decisively and change the law.
In a new account of how New Zealand became nuclear-free, Peace, Power and Politics, Leadbeater writes that politicians and historians "often write the public out of the story. But here - as in the case of almost every other major shift in government policy in our history - the spadework was carried out by the little people who wrote letters, marched and put their bodies and boats on the line ... It was a David and Goliath moment, but David did not stand alone."
The backdrop to Leadbeater's book recalls tense political moments, the frustrations of the military and foreign policy bureaucracy and the superpower pressure piled on New Zealand to whip it into line over ship visits. But at its core is the story of how a popular movement, led by determined, committed activists, achieved an enduring change in the country's foreign policy and entrenched the idea of "nuclear-free NZ" in the national psyche.
It is a colourful history, for the cause was supported by some of the nation's leading artists. A lot of their efforts, with the posters pasted on urban walls at the height of anti-nuclear activism, are reproduced in the book.
That Leadbeater was one of the leading lights is perhaps not surprising. As a daughter of one of New Zealand's pioneering feminists, the children's author Elsie Locke, dissent is part of her DNA. Locke, together with her second husband, Jack, a lifelong communist, shared a modest cottage beside the Avon River in Christchurch with their children - Maire and her sister Alison, and brothers Don and Keith, who became a Green MP.
Elsie shared her husband's communist beliefs until she left the party in 1956, upset at the brutal Soviet invasion of Hungary. About then Maire, at just 10, came to the attention of the Security Intelligence Service, who kept a Cold War watch on her parents. Leadbeater's redacted and declassified SIS file, released in 2008, recorded that she delivered a copy of the People's Voice, the Communist Party newspaper, to an address in central Christchurch. Nearly 50 years later the spy agency was still reporting on her. The last file reference mentioned plans to join a peace march in 2002, which Leadbeater assumes was about Iraq.
The SIS file entries illustrate Leadbeater's tireless devotion to political causes - the rights of indigenous people in East Timor, the Philippines, New Caledonia, Tahiti and now West Papua, the mountainous Indonesian-ruled territory where New Zealand is helping to train local police.
The activist, now 68, wrote the anti-nuclear book partly to complete a project her mother started. Elsie Locke's book, Peace People: A History of Peace Activities in New Zealand, closed off in 1975. Her daughter carries the story through to today.
Leadbeater accepts the high tide of activism has receded since the heady days of the Buchanan, when 300 peace groups flourished, flotillas assembled at the hint of a radioactive rumour and hundreds came to rallies.
But she says there are plenty of campaigns for activists to wage for ethical and humanitarian aims.
"For years we had protests at Waihopai [the spy station near Blenheim which is part the Five Eyes intelligence sharing network]."
She says that the task of activists is "really about challenging the power over our lives that we've given away".
In the past decade or so, Leadbeater has become more deeply involved with independence and solidarity issues in the South Pacific, and especially West Papua. She argues NZ has dropped the ball in its neighbourhood and could be more actively engaged in trying to resolve regional conflicts.
Leadbeater believes the work which helped broker peace in Bougainville after a decade of war claimed at least 8000 lives serves as a model worth trying elsewhere. New Zealand took the lead in the dispute and, against a background of Maori protocol, invited leaders from the rival factions for talks. The resulting Burnham Declaration has held firm for 15 years.
Journalist John Pilger once called NZ the West's "problem child" for standing up for anti-nuclear ideals with "principled audacity". "We still have that potential," she says. "We ought to be doing far more."
See also: Tracking a time of transformation