Speaking to Channel 4, activists criticised Cameron's decision to attend the Commonwealth Heads of Government Meeting in Sri Lanka in November.
The director of Tamils Against Genocide (TAG), Jan Jananayagam, said:
"I am disappointed as a British citizen and I am embarrassed for Britain that David Cameron is unable to muster a fraction of Canada’s leadership on this. I think we will look back to regret this as an historic error. It is a sort of death knell for the Commonwealth."
Suren Surendiran of the Global Tamil Forum said:
"British Tamils are disgusted that our Prime Minister would even contemplate being in the company of the Rajapaksa family, members of which are being accused of being war criminals."
Also speaking to Channel 4, Fred Carver from Sri Lanka Campaign for Peace and Justice, said:
"David Cameron has shown that he is not interested in the Commonwealth being a community of shared values; what possible meaning can being in the Commonwealth have if it is headed by Mahinda Rajapaska?"