As usual the police figures were a lot lower than other estimates, tamilnet.com reckons 200,000+ which was an amazing two thirds of the British Tamil population!
In a historic show of solidarity, more than 200,000 British Tamils, nearly two thirds of Tamils resident in Britain, marched through the streets of London Saturday demanding immediate ceasefire and recognition of Tamil Eelam. Sparked off by the initiative of second generation diaspora Tamil youth and students four days earlier, the Saturday’s march became an unprecedented rallying point for the entire community, attracting the old students associations of the educational institutions of Eezham Tamils, functioning in London. The spirited participation of teens and mothers with babies in pushchairs significantly marked the level of community involvement in the agitation.
Whatever figure you want to choose it was a huge event and demands a serious and engaged response from the government. If only they can stop shipping arms to the Sri Lankan military for a few seconds.