(Transcript from World News Australia Radio)
At issue is the growing pressure for Sri Lanka to address the allegations of human rights abuses by its troops at the end of the country's bloody civil war in 2009.
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There have been regular references to allegations of human rights abuses by Sri Lankan government forces and Tamil Tiger rebels in the final stages of the war in 2009.
A United Nations panel concluded in 2011 there were credible reports that government forces killed Tamil civilians by widespread shelling, and by denying humanitarian assistance.
The panel also concluded there were credible allegations that the Liberation Tigers of Tamil Eelam had used civilians as human shields, and killed people trying to escape from the war zone.
At the last CHOGM held in Perth two years ago allegations of war crimes in Sri Lanka were a prominent issue.
But when the Heads of Government meeting ended, the only reference to Sri Lanka in the final communique was the fact that it would be the host of the next meeting, in two years.
Now those two years are up but the issue of human rights abuses has not gone away.
Those not attending include Canadian Prime Minister Stephen Harper and Indian Prime Manmohan Singh.
India, with 62 million ethnic Tamils in its southern state of Tamil Nadu, was under immense pressure to boycott CHOGM.
Mr Singh's absence will be a major blow to the credibility of the organisation as India is the Commonwealth's largest member.
But India's Foreign Minister, Salman Khurshid, denies any domestic political pressure.
"Earlier also there have been instances when our Prime Minister has not been able to attend the Commonwealth meet in the past.
"Often there are times when we need the Prime Minister to discuss the political situation of the country and other matters of importance due to which he has to change his plans.
"Last year also it was the Vice President of the country who went for the meeting and earlier, many a times it was the Foreign Minister who represented the country at the meet."
Canadian Prime Minister Stephen Harper says he's disturbed by ongoing reports of intimidation and incarceration of political leaders and journalists, harassment of minorities, reported disappearances and allegations of extrajudicial killings.
But British Prime Minister David Cameron will attend, despite protests from Tamils in Britain, saying he will raise the human rights issues with Sri Lankan President Mahinda Rajapakse.
Britain's Foreign Minister, William Hague, says there are serious questions about war crimes allegedly committed during Sri Lanka's civil war.
Mr Hague says the UK can raise this matter, and other serious issues, only if it is there.
"We have decided that if we were to stay away from this meeting in Sri Lanka it would damage the Commonwealth without changing things positively in Sri Lanka. Now we need to be there at the Commonwealth meeting. So we are discussing there the future of international development, how we are helping developing countries. I want to discuss with the whole Commonwealth our efforts to prevent sexual violence in conflict. Rather than sit in London than talk about it. We will be there."
Australia's Foreign Minister, Julie Bishop, says she agrees with Mr Hague.
She says isolating Sri Lanka will not solve anything.
"I have been having ongoing discussions with the Sri Lankan government. And I have encouraged all member nations of the Commonwealth to attend the Commonwealth Heads of Government meeting to engage with Sri Lanka on these issues rather than isolate Sri Lanka. It's been an ongoing discussion and I'll continue to work purposefully with the Sri Lankan government in relation to matters that have arisen as a result of the end of the 30 year civil war. Progress has been made but there's clearly more to be done."
South African peace campaigner Archbishop Desmond Tutu says pressure must be applied to the Sri Lankan government.
Archbishop Tutu says the issue of alleged war crimes needs to be addressed.
"If there are enough reasons to suggest that the Sri Lankan government has not been doing things with integrity, then I think the world has to apply all the screws that it can."
Every two years Commonwealth leaders meet at the Commonwealth Heads of Government Meeting to discuss global and Commonwealth issues, and agree collective policies and initiatives.
Sri Lanka's Opposition leader, Ranil Wickremesinghe, says the meeting is an opportunity to push for change.
"We are getting onto the road to agitate that the rights given to the people of the Commonwealth, which must be enforced by the country that is the chairman, must be given to the people here. Our sovereignty, our fundamental rights, have been taken away by the Rajapakse regime."
The Sri Lankan government says its rights record has improved since the war and it rejects the criticism as unsubstantiated.
The Colombo meeting will be the first CHOGM not attended by Queen Elizabeth the Second in 40 years.
Prince Charles will be attending in her absence.