David Cameron and other Commonwealth leaders were condemned yesterday for ignoring Sri Lanka's appalling human rights record and preparing to jet into the capital Colombo.

Unless they take action Sri Lankan President Mahinda Rajapaksa will be appointed chairman-in-office - representing the 53-nation Commonwealth until 2015.

His government is implicated in serious human rights abuse both during and since the end of Sri Lanka's brutal civil war.

The United Nations estimates that 40,000 members of the Tamil minority were killed during the bloody military clampdown in 2009 which ended a 26-year rebellion by Tamil Tiger separatists.

The prime ministers of India, Canada and Mauritius are boycotting the Commonwealth heads of government meeting.

Campaigners slammed the other member states for going about business as normal.

Amnesty International accused Sri Lanka this week of a major crackdown on free speech.

Sri Lankan troops blocked scores of family members of "disappeared" people from attending a human rights vigil in Colombo on Wednesday.

Amnesty called it "the latest move to stifle freedom of expression and assembly" before the weekend meeting.

"This is a blatant attempt by the authorities to stifle people's right to peaceful protest," top Amnesty official Steve Crawshaw said.

"The government has in recent years done everything in its power to silence dissent.

"The Commonwealth has been shamefully silent throughout this and has yet to condemn the human rights violations that are still so clearly business as usual for Sri Lanka.

"Given Sri Lanka's atrocious human rights record and its refusal to address ongoing violations, the country should not have been allowed to host (the meeting) in the first place."

Labour leader Ed Miliband joined the calls for Mr Cameron to make sure Mr Rajapaksa is not appointed to lead the Commonwealth.

Mr Miliband, who had previously urged the PM to boycott the meeting, wrote in the London-based Tamil Guardian that he had "serious reservations" about Mr Rajapaksa's suitability for the group's top job.

"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," he said.