Last Thursday, some of them, including peacemakers like Pat Dodson, Noel Pearson, MP Ken Wyatt and Marcia Langton joined with four like-minded pollies plus legal minds such as Fred Chaney and Mark Leibler to participate in a modern day indigenous ritual - delivering a report to Canberra.

The Prime Minister, Julia Gillard, had asked a 19-member expert panel to suggest how indigenous people should be included in the constitution and they told her: ditch the race power meant to benefit Aborigines but which has been used to discriminate against them, and instead acknowledge the need to secure their advancement. They also wanted recognition that the continent and islands were first occupied by Aborigines and Torres Strait Islanders, whose languages are the original Australian tongues and that the people have a continuing relationship with their traditional lands and waters.

There were smiles and tears as Gillard urged the people of Australia to say ''yes'' to constitutional change at some future unknown date.

But a week later, the smiles and tears could turn to shouts and chants as another indigenous ritual is revived. According to veteran campaigner Michael Anderson, incipient fury over all that land lost and never regained is expected to boil over in a protest march through Canberra streets on Australia Day to the Aboriginal tent embassy.

While the Government talks with ''hand-picked'' indigenous representatives, the old guard of the 1970s Black Power movement will be in town to mark the embassy's 40th anniversary, and this year ''the Aboriginal political movement will be ramped up and become more aggressive,'' Anderson says.

There is still anger over the exclusion from the constitution, the Northern Territory intervention and the failure to recognise indigenous sovereignty in a treaty. This week, old stagers like Anderson, Gary Foley and Les Malezer intend to use the tent embassy's birthday to show how to harness it.

They used manila folders to make the first sign declaring ''Aboriginal Embassy,'' tying it with shoelaces to a beach umbrella which they planted in the Old Parliament House lawn as protection from the weather in that fine old 1970s tradition of a sit-in protest, Anderson recalls.

The only man alive of the four original tent ''ambassadors'', he remembers Noel Hazzard, photographer on the communist newspaper Tribune, driving them to Canberra. The black poet Kevin Gilbert rustled up $70 from the communists for food.

Gary Williams, one of the seasoned indigenous protesters in Sydney who called for young volunteers to be envoys to the nation's capital, recalled: ''Our parting words were: 'See if you can get some photographs for the local paper, even if the police kick you off.' We were just thinking it was going to be a few hours and the police would have them removed.''

Many thousands of photographs, words and film footage later, the Aboriginal tent embassy is still there, a huddle of shelters, sheds and vans which will morph next week into a small canvas township where smoking ceremonies and corroborees, big-screen Skyping and sessions on sovereignty will be held to celebrate 40 years of survival.

Anderson, who was welcomed to the microphone at the Occupy London rally as a sit-in hero, told the police recently that 1500 would attend the commemoration, but the police said they were catering for 6000. The word this week was 300 were coming in a convoy from north Queensland alone.

Ellie Gilbert, widow of the poet whose ashes were buried at the embassy site in 1993, said: ''We just don't have a clue. People want to come. It just depends who can get fuel in the car and get here.''

Unlike the initial reactions to that first gathering, no one intends to turf the campers out. Instead, the ACT government has given funds to help celebrate the anniversary of a robust, if ragtag site now on the tourist coach route. The Australian Heritage Council registered the tent embassy site on the National Estate 17 years ago, making it almost respectable.

Gary Williams becomes religious when he talks about the history. A new wave of young activists inspired by the Black Power movement in the US were hungry for the federal government to grant land rights after the Northern Territory Supreme Court found that the law did not recognise Aboriginal title to land. They responded with fury when prime minister Billy McMahon announced on January 25, 1972, that his government would create leases but not grant freehold title.

''He was playing semantics,'' Williams says. ''We thought we'd better get down there … The land rights campaign was a series of words and this action solidified things and people saw it in Canberra. You could say the words were made flesh.''

Gary Foley, described as ''troublemaker, teacher and teller of tales'' for his show Foley, which opens at the Sydney Opera House on Tuesday, says: ''It was only ever intended to be a momentary stunt, but it accidentally found loopholes in Canberra law which enabled it to stay there. There was no law against camping on the grounds of Parliament.''

The embassy, whose story he will tell laced with expletives and film, shattered claims that the local black power movement was violent and racist, as it mounted an effective, peaceful protest, he says.

''We could stage a demonstration like that with style,'' he said. ''People loved the fact we were able to get away with it with no violence. It made the government look like fools and appealed to the larrikin streak.''

When the ''momentary stunt'' had stretched into six months, the Coalition gazetted an ordinance banning squatting on the parliamentary lawns and 60 police removed the tents, arresting eight people, including Foley. Days later, there was a bloody confrontation when agitators tried to re-establish the embassy.

''It was the most violent demonstration I have ever been in,'' Anderson says. ''Three hundred police came marching around German Nazi style from the back of the House. We were just shocked at the way they came out in these big boots and uniforms and circled around us.

''Eighteen of us went to jail and 36 police officers were treated in hospital. [Activist] Paul Coe was the main one hurt. They launched a jackboot straight into the crown jewels … I had a cut lip from a flying fist.''

Anderson was thrown into a police wagon on top of the Bellear brothers, Sol, who became a leading NSW public servant, and Bob, the late judge.

Despite the occasional fracas, life is quieter on the lawns now. Anderson and fellow commemoration organisers have secured marquees as dormitories, portable toilets and shower blocks, bottles of drinking water, meat, fruit and vegetables, barbecues and art materials for the children.

Where the old protesters fought with police, there will be an on-site massage therapist and doctors.

However adept the old radicals have become at managing peaceful crowds, like the sacred fire burning at the site they want to show that the flame of protest has not died.

On Wednesday there will be a corroboree dedicated to the ''last day of freedom,'' more than two centuries after the eve of the First Fleet's arrival in Sydney Cove, and there are plans for hard talk about what Australia still needs to do.

''The position of our people is worse than in 1972,'' Anderson says. ''We've gone a long way backwards. You can talk about the bricks and mortar and doctors, but people would have done it anyway. It was a program made on the part of the people, who created an Aboriginal education strategy.''

Research he and fellow activists conducted in London revealed Queen Victoria recognised Aboriginal sovereignty in the Pacific Islanders Protection Act of 1875 and they argue that land they lost after that date must by law be returned.

Anderson is part of a ''grassroots'' movement, a mob of outsiders acting separately from the high-profile activists who are more willing to sit inside the government tent, including the members of the new, independent but publicly funded National Congress of Australia's First Peoples.

Les Malezer, a long-time street campaigner who is now co-chairman of the congress, which is hosting a two-day ''people's forum'' in Canberra from Tuesday, says this will be a chance to speak about the 1972 protest issues of land, sovereignty and self-determination.

Calls for a treaty are likely to resound again, he says. Robust debate about indigenous affairs is likely to be back since Gillard received a report on Thursday from an ''expert panel'' calling for a referendum on indigenous inclusion in the constitution, he says.

''I don't think the treaty call has ever gone away. It's just a case that government tends to destroy the advocacy of Aboriginal rights.''

Foley, who describes the tent embassy as ''by far the most successful Aboriginal action of the 20th century, says: ''The land rights movement never achieved its aim.''

Most of the old indigenous activists agree that although the Mabo decision brought recognition of native title, it has not conferred land rights on the Aboriginal masses.

In his stage show, part of the Sydney Festival, Foley is telling how that battle was almost won and lost. Less than a fortnight after the tent embassy was established, the then opposition leader Gough Whitlam visited and promised his government would allow ''ownership of land by tribal communities,'' according to Foley. ''When he did grant land rights], it was for a tiny crew in the Northern Territory because Whitlam was too gutless to take on the state governments.''

In the 1980s, when Labor had national uniform land rights legislation including freehold title in its platform, Bob Hawke as prime minister reneged. Then Western Australian premier Brian Burke, under massive pressure from mining interests, told Hawke, in Foley's words, ''you've got to forget those Abos''.

The embassy marked the beginning of belief in an Aboriginal nation transcending old ideas of caste which dictated who could be considered truly indigenous, comparing ''full-bloods'' with ''mixed-bloods,'' James Cook University historian Russell McGregor says.

The embassy has been torn down several times and been reborn. It has been replicated in a house at Mugga Way, Red Hill, at Victoria Park and Mrs Macquarie's Chair in Sydney, in London, Brisbane and Adelaide.

International visitors included an Irish Republican Army representative who donated a linen handkerchief to the cause, according to the late historian Scott Robinson. Two middle-aged Aboriginal lovers and protesters, Arthur and Rose Kirby, married there and smoke from its sacred fires was taken into Old Parliament House during the 1998 Constitutional Convention.

On Thursday night, Foley hopes to Skype on-stage with the old campaigners. He is 62 and does not want to say what should come next. ''It's for the younger generation to get off their arses and get their acts together and fight their battles. Old dogs like me have had our day,'' Foley says.

Williams believes the embassy is, in a way, unchanged: ''It's still reminding people that we are alienated in our own land.''