Tamil activists are calling for an international arrest warrant for Mahinda Rajapaksa, the Sri Lankan president.
To many Tamils, Rajapaksa is a war criminal responsible, as commander in chief of Sri Lankan forces, for the deaths of thousands of Tamil civilians in a civil war that ended in 2009.
Rajapaksa was greeted by Tamil protestors as he arrived in London on Monday night.
Demonstrators accuse him of war crimes linked to the civil war that ended last year, with the surface of new video footage taken during the conflict could inflame Tamil anger further.
Al Jazeera's Jonah Hull reports from London.
