Ed Miliband has called on Commonwealth leaders to block Sri Lanka's President from being automatically appointed as the group's chairperson-in-office.
The Labour leader reiterated his call for David Cameron to boycott a Commonwealth summit being held in the country from today, citing Sri Lanka's "lamentable" human rights situation.
The country's President, Mahinda Rajapaksa, is due to assume the position as chairperson by default at the summit's conclusion.
"There are many, myself included, who have serious reservations about President Rajapaksa’s suitability for this important role," Mr Miliband said.
"So at this summit this week, unless we see real and meaningful change on human rights in Sri Lanka, David Cameron should work with other Commonwealth leaders on securing an alternative candidate for chairperson-in-office."
He warned that the summit could become a "flashpoint for protest" in the country, which was ravaged by a bloody civil war until four years ago.
"Because we all believe the Commonwealth must remain relevant, the Prime Minister must make sure he defends the place of freedom, democracy and human rights at its core," Mr Miliband said.
Several countries, including India and Canada, are avoiding the summit amid concerns over alleged war crimes by the regime against separatist Tamil groups at the end of the 26 year conflict.
But Mr Cameron earlier defended his decision to attend, insisting he would seek a meeting with President Rajapaksa to raise his concerns about the country's human rights record.
