Tamil protesters are staging a demonstration outside the Mansion House in the City of London.
The Sri Lankan President Mahinda Rajapaksa had been due to address a Diamond Jubilee Commonwealth Economic Forum, but the morning session of the event has now been cancelled.
The protesters accuse Rajapaksa of running a dictatorial regime which represses the Tamil people.
A spokesman for Tamil Solidarity said:
"This butcher and his dictatorial regime is still brutally repressing the Tamil-speaking people and trampling democratic rights. Britain has enough war criminals without Rajapaksa, with the blood of hundreds of thousands on his hands, 40,000 in the last weeks of the war alone, being invited for the Jubilee."
More top news
The Mayor of London is one of several familiar faces popping up when the show returns to screens for its fifth series in November.
Here is a timeline of some of the key events in the debate over expansion of airport capacity.
More than 700 households were today bracing themselves for a government decision which could see their homes bulldozed.