Leaders of the Commonwealth group of mostly former British colonies met on Friday for a three-day summit under pressure to get tougher on human rights abuses by members or risk losing its purpose as a group.

The 85-year-old Queen Elizabeth opened the meeting of leaders of the 54 states of the Commonwealth, home to 30 percent of the world's population and five of the G20 leading economies but struggling to make an impact on global policies.

The leadup to the summit has been dominated by pressure to take a stronger line on human and political rights abuses. A confidential report to the group warned than unless it did, the Commonwealth risked becoming pointless as an organisation.

Australian Prime Minister Julia Gillard, in her opening speech, touched on the issue when she said it needed to ensure that those member nations that fall short (of the group's values) understand that their peers want to see change.

Much of the debate has focussed on Sri Lanka and international demands that it allow an independent inquiry into accusations of war crimes during its 25-year civil war, especially in its final months in 2009.

Sri Lanka says it will wait for the results of its own investigation next month, calling the pressure over human rights a propaganda war waged by the defeated Tamil Tigers.

A senior Commonwealth official said foreign ministers on Thursday failed to agree on a key recommendation in an eminent persons report that the group set up a rights commissioner.

Canada, home to a large ethnic Tamil community, has said it will boycott the 2013 Commonwealth summit in Sri Lanka, unless the host country improves its human rights record.

Today, Commonwealth leaders are faced with a choice - reform the Commonwealth so that it can effectively address human rights violations by its members, or risk becoming irrelevant, said Madhu Malhotra, Amnesty International's Asia-Pacific Deputy Director.

Prime Minister David Cameron dismissed suggestions that the Commonwealth was no longer of much use.

We live in a world of networks and this is a great network: a third of the world's population, 54 different countries across six continents, he told reporters in Perth.

But not just a network, a network with values about promoting human rights and democracy and freedom.

ABORIGINES CLEANSE OPENING CEREMONY

Aborigines cleansed the opening ceremony by waving smoke from burning grass over leaders as they arrived. Local Noongar Aborigines welcomed the leaders to their traditional homeland.

In a stark reminder of the clash of cultures, Aborigines refer to British white settlement of Australia as the invasion.

About 500 people, protesting a broad range of issues, demonstrated in Perth but were kept well away from the leaders by a large contingent of police in the central business district, dominated by office blocks of the mining companies that are the backbone of Western Australia's economy.

Smaller countries within the group, many at risk from the effects of global warming, are pressing for a strong statement ahead on next month's international summit of climate change in the South African city of Durban.

There have also been calls on leaders to help to end the practice of child brides. Twelve of the 20 countries with the highest rates of child brides are in the Commonwealth.

And health advocates say laws in 41 Commonwealth states making homosexuality a crime breached human rights, hindering the fight against HIV-AIDS. Commonwealth states represent 60 percent of the world's HIV-AIDS population.

(Additional reporting by Mohammed Abbas, Writing by Jonathan Thatcher; Editing by Ron Popeski)