London Marathon security tight following Boston attacks
Security at this year's London Marathon has been tightened following bomb attacks in Boston.
Thousands of people lined the streets to see the athletes set off from Blackheath, many wearing black ribbons on their vests in memory of the victims of last Monday's explosions.
Hundreds of extra police officers - 40% more than last year - have been drafted in to reassure runners and spectators.
Jon Brain reports.