A spokesperson for Number 10 has said that the Prime Minister David Cameron will call for an international inquiry, if Sri Lanka does not deliver an independent investigation into accusations of war crimes and crimes against humanity.

"We have consistently called for an independent inquiry into the allegations,” the spokesperson said.

“To date, that has not happened. And the PM believes that in the absence of an independent investigation, an international inquiry would be needed.”

The Foreign Secretary William Hague said in an interview with Channel 4 that Britain would work with the UN on any future international inquiry.

Saying that “terrible things” had happened in Sri Lanka and “well substantiated allegations” had been made, Hague insisted that a boycott would be damaging to the Commonwealth and Britain’s engagement would help change things in Sri Lanka.

Pressed by presenter Jon Snow on tangible outcomes he expected to see, Hague said if Sri Lanka does not deliver an independent, credible, thorough inquiry, Britain, like many other countries would push for an international, independent investigation.

"If they don't set one up then we, and the rest of the world... will want to support an international investigation,” the Foreign Secretary said.

Asked by Snow on how long Britain is going to wait for a credible Sri Lankan inquiry, Hague said that a process was already in place at the UN Human Rights Council, initiated by High Commissioner Navi Pillay, with a deadline in March, and the British government would work with the UN on future moves regarding an international investigation.

But Hague continued to defend the decision to attend the summit, comparing engagement with Sri Lanka to engagement with Burma.

"Have terrible human rights been committed [in Burma]? Yes they have. But it hasn't stopped us engaging to some good effect. I think we have to try that with Sri Lanka and acknowledge that some good things have been done as well."

"I will argue to the whole of the Commonwealth that it has to support our efforts in preventing sexual violence in conflict and I wouldn't be able to do that if I wasn't at the meeting, and that is why we have to be at the meeting, not sitting in London isolating ourselves from the argument."