David Cameron was set to attend a Commonwealth summit in Sri Lanka this week.
The leaders of India and Canada are boycotting the event because of the country’s human rights record.
Prince Charles is also attending the Commonwealth summit.
The Sri Lankan government has been behind kidnappings and torture, on top of its brutal repression and war crimes against the Tamil minority.
The charity Freedom from Torture has examined 120 incidents that took place after the war against the Tamils ended in 2009.
Two doctors from the charity Medact have seen more than 60 cases of Sri Lankans branded on their bodies with hot metal rods since the war ended.