The Commonwealth Games in Glasgow risk being overshadowed by a human rights row if Sri Lanka's president is allowed to become chair of the 53-nation organisation, Labour has said.

Shadow foreign secretary Douglas Alexander called on David Cameron to push for a review of whether Mahinda Rajapaksa should be granted the position when he meets fellow leaders this week.

The Prime Minister is resisting pressure to boycott the Commonwealth Heads of Government Meeting (Chogm), being hosted by the island next week, over war crimes and other alleged violations.

The UN High Commissioner for Human Rights Navi Pillay warned in August that Sri Lanka - considered a "country of concern" by the Foreign Office - was heading in an "increasingly authoritarian direction".

Critics say any engagement with the regime - which has failed to meet international demands for an independent inquiry into events at the end of a bloody civil war in 2009 - amounts to "collaboration".

Mr Cameron has met with representatives of the minority Tamil community to explain his decision - telling them he believed his visit would help "shine a spotlight" on their concerns.

Among assurances they claimed to have secured was that the UK would consider raising the issue of breaking the tradition that summit hosts assume the chairing role for the following two years.

In a letter to the PM, shadow foreign secretary Douglas Alexander sought clarification of the position - saying Labour would support any efforts to address the issue.

"It was reported that you are now willing to consider Labour's call for the automatic passing of the Commonwealth's Chairperson-in-Office to President Rajapaksa following the summit to be reviewed," he wrote.

"Serious questions will be raised by the prospect of President Rajapaksa representing the Commonwealth on an international stage.

"Failure to address this would run the risk that upcoming events such as the Commonwealth Games - which will be a proud moment for Scotland and a celebration of world-class sporting achievement - risk being a time of sustained questions about president Rajapaksa's Commonwealth role and human rights record of his government.

"If the Government is now willing to address this issue, you would have Labour's support, but given the apparent reluctance to accept the need for review up until this point, I hope you will understand the need for urgent clarification on this matter."

Mr Alexander also asked about claims by the Global Tamil Forum - which were firmly rejected by Number 10 - that Mr Cameron was to consider downgrading the delegation.

Downing Street insists the premier was clear that both he and Foreign Secretary William Hague would be at the meeting - which is also being attended by the Prince of Wales, on behalf of the Queen.

"Can you clarify if the British delegation is indeed to be downgraded, and if so, which government minister will now not be travelling to the summit?" Mr Alexander asked.

Labour has urged the Government to follow the lead of Canada's prime minister Stephen Harper by staying away from the 53-nation summit.

Mr Alexander said it was "inexplicable that the Government chose to hand away its influence six months ahead of the summit even taking place" by confirming the senior pair's attendance.

He also questioned what the "consequences" were for the regime promised by Deputy Prime Minister Nick Clegg if it failed adequately to address rights issues before the high-level gathering.

"In light of your public acknowledgement that the Sri Lankan authorities have failed to make sufficient progress on human rights in the run up to the summit, can you set out what have been the specific 'consequences' of this failure, or if there have been none at all, can you explain why?" he asked.

Mr Cameron has indicated he backs an international inquiry into the brutal put down of the Tamil Tiger independence movement if the Rajapaska government fails to commission an independent inquiry.

Ms Pillay has warned of outside action if the regime does not take "comprehensive measures" to address violations by the time of her full report on the country in March.

Both sides are accused of war crimes in the intense final months of the civil war in 2009 - in which the UN estimates up to 40,000 civilians died.

They include the indiscriminate shelling by government forces of so-called "no fire zones" where the population was told to seek shelter - something the regime disputes.

Mr Rajapaska set up a "lessons learnt and reconciliation commission" in 2011 under global pressure but critics say few of its recommendations have been implemented.

The House of Commons Foreign Affairs Committee report recently found "scant evidence of progress in political and human rights".

"Four years after the conflict, no-one has been held to account for grave allegations of war crimes and sexual violence, journalists are routinely intimidated and thousands of people have yet to find out what has happened to their missing relatives," Mr Cameron said.

"I want to see that change. And I do not believe boycotting the Commonwealth meeting will achieve that. The right thing to do is to engage."

The Prime Minister is scheduled to become the first head of state to visit the Tamil-dominated north of the island since independence in 1948 to speak to people affected by the conflict and its aftermath.

Mr Hague said it would be "gravely damaging" to the Commonwealth if the British Government failed to attend.