The protests erupted a day after after the country's President Mahinda Rajapaksa was stopped from addressing students at UK's prestigious Oxford University and Channel 4 aired alleged footage of widespread human rights violations by Sri Lankan armed forces in the closing stages of the decisive war against Tamil Tigers.
"Down with UK's Sri Lankan policy," and "Don't support terrorists", shouted the marchers led by Housing Minister Wimal Weerawansa, outside the British High Commission. Waving Sri lankan flags, they attempted to forcibly enter the premises but were barred by police.
The minister accused the Whitehall of silently supporting the sympathisers of vanquished Tamil Tigers by allowing them to stage protests against Rajapaksa during his state visit to England.
"We have taken to the streets against the uncivilised act of the British Government," Weerawansa said and described the protesters against Rajapaksa as "terrorists".
"How can UK Government allow LTTE supporters to demonstrate when they have banned Tamil Tiger group in England," he said, accusing London of being partisan to the LTTE.
The protesters in England accused Rajapaksa of war crimes, while crushing Tamil separatists in the country last year. They called for arrest of Sri Lankan President and his trial by international jury.
The protests in Colombo came as Britain joined its Western allies, UN and rights groups, to call for an independent probe into the possible human rights violations during its civil war.