A complete contrast in the reaction to Channel 4 in the north of Sri Lanka, reports Jon Snow. "Up here among the Tamils, if they see that you're from Channel 4 they immediately run forward and grasp your hand."

Mr Cameron is in Jaffna, in the traditionally Tamil part of Sri Lanka, and is accompanied by journalists including Jon Snow. His first visit in Jaffna was to a library , where he met with Chief Minister CV Vigneswaran.

However, outside there were two protests taking place, as Jon Snow describes.

"The first, very ordered and very similarly printed protest banners. Some of the slogans read 'time to investigate British colonial atrocities'," he said.

"Then our attention was drawn to a rather bigger demonstration much further down the road and that involved a large number of women holding photographs and letters depicting what had happened to their lost loved ones.

"There were many women in tears hanging onto journalists, including myself, begging us to take letters and take them to David Cameron.

"In the end there were an armful of letters pleading for some sort of action,. But most of these young men as they were when they surrendered to the military, have never been heard of again."

As the prime minister went to leave the protesters broke through police blockades and surrounded the vehicles that were leaving.

As Channel 4 News showed in the film White Van Stories, shown on 14 November, enforced disappearances of Sri Lankan people continues to this day.

Mr Cameron and the journalists then headed to the newspaper offices of a Tamil newspaper, where he heard about how printing presses were recently destroyed with bullets fired through them.

Mr Cameron told staff at the newspaper of how impressed he was with their bravery.

The journalists then moved onto a refugee village were people are "still living in pretty meagre circumstances."

On the way to the refugee village, the journalists and Mr Cameron came across another pro-government demonstration.

Mr Snow said the prime minister seems "pretty concerned by what he’s seen, but I don't think he was surprised."

Mr Cameron said he would be telling President Mahindra Rajapaksa - who has himself been accused of war crimes connected to the end of the Sri Lankan civil war, in which the ruthless Tamil Tigers movement was crushed by the military - that he must hold an independent inquiry into allegations of human rights violations.

Mr Cameron said that if no such investigation was forthcoming, he would urge the United Nations to conduct and international, independent investigation.

Channel 4 News has been met by both hostility and praise in Sri Lanka, due to revelations of war crimes allegations since the end of the civil war.

But Jon Snow said in the Tamil-dominated north, he was greeted by pulling who "run forward and grasp you hand and hug you".