There has been a show of solidarity at the London marathon for those who were killed and injured in this week in Boston. An estimated 36,000 people will take part in the London race this year. It is not the biggest marathon in the world, but is certainly one of the most colourful. As a precaution, this year there was also a massively boosted police presence. Al Jazeera's Nadim Baba reports from London.
