There is always disquiet when imperialist world leaders guilty of supporting aggressions that have caused hundreds of thousands of deaths set themselves up as moral arbiters.

David Cameron not only was fully behind the unjustifiable invasions of Afghanistan, Iraq and Libya but would have had Britain bombing Syria if the House of Commons had not shown greater judgement.

However, in the case of Sri Lanka, President Mahinda Rajapaksa's refusal to acknowledge the scale of the cold-blooded massacre of Tamils at the end of the country's civil war makes his appointment as Commonwealth chairman-in-office totally unacceptable.

Many Liberation Tigers of Tamil Eelam leaders were taken prisoner and filmed in the custody of Sri Lanka's armed forces.

Their bullet-riddled bodies were pictured later and portrayed as having been killed in battle, which is as far-fetched as similar claims made by Britain's allies in Libya over the murder of ousted leader Muammar Gadaffi.

There was also ample evidence that female members of the Tamil Tiger fighters had been raped before being killed.

Even the then head of the Sri Lankan army, Sarath Fonseka, testified to having been authorised by defence secretary Gotabaya Rajapaksa, the president's brother, to put captured Tiger fighters to death.

The president claims to be committed to close relations between the island's two main communities, the Sinhalese majority and Tamil minority, both of whose languages he speaks.

But his decision to turn his back on the People's Alliance with the Communist Party and the Lanka Sama Samaj Party in favour of linking his Sri Lanka Freedom Party with the Sinhalese nationalist Janatha Vimukhti Peramuna (National Liberation Front) in a United People's Freedom Alliance in 2004 marked a sinister turn.

The JVP had denounced an earlier joint ceasefire as treason and opposed any concept of autonomy for the Tamil minority.

Nor was it only the military and political leaders of the Tamil Tigers that were wiped out in the orgy of slaughter ordered by Rajapaksa's forces.

It is generally accepted that 40,000 Tamil civilians were killed in northern Sri Lanka during that macabre civil war endgame.

Rajapaksa flatly denies any human rights violations then or since, insisting that there is a system in place to investigate allegations of rape or torture.

However, UN human rights council commissioner Navaneetham Pillay charged earlier this year that Sri Lanka has become increasingly authoritarian and that, since the end of the civil war four years ago, democracy has been undermined and the rule of law eroded.

The UN body has urged Sri Lanka to investigate widely reported breaches of human rights committed during the final phase of war with the Tamil Tigers, but it is clear that this will not take place.

The Colombo government seeks to play the independence card, insisting that national sovereignty dictates that it should not acquiesce even to answering questions about a human rights deficit in Sri Lanka.

One MP from JVP, Vijitha Herath, proposed last weekend that Sri Lanka should withdraw from the Commonwealth on the grounds that discussing who should be its chairman "indicates that Sri Lanka continues to remain a colony."

Whether Sri Lanka chooses to remain a Commonwealth member is a matter for the people of that country.

However, there should be no question of a blood-soaked butcher, President Rajapaksa, taking its chair and representing it in world forums for the next two years.