The London Marathon is now underway, with many runners wearing black ribbons in honour of the victims of the Boston bombings.
The elite women's race began in London's Blackheath at 9am, followed by the elite wheelchair race at 9:20am and the elite men's race and mass race at 10am.
BBC News reports that a 30-second silence will be held at the start of the mass race, at 9:57am, for those killed and injured in Boston.
As well as the 35,000 competitors, half a million people are expected to line the route around London. Hundreds of extra police officers, around 40 per cent more than last year, have been called in to help reassure runners and spectators.
Sky News reports that Richard Inchley, who has been registering runners, says that the Boston bombings have not deterred competitors from taking part. Every runner was given a black ribbon to wear during the race.
He says: "People are more determined than ever to take part, and I can't think of a single person who wasn't eager to wear the ribbon."
According to BBC News, The Metropolitan Police reviewed security plans after the Boston attacks, and organisers say that there is no known threat to the race.
Chief Superintendent Julia Pendry, who has headed marathon security for five years, said that this year more search dogs will be deployed and asked spectators to keep their belongings with them to prevent security alerts.
She told the BBC: "There is no link between the Boston Marathon and the London Marathon and there is no change to the threat level at this time to London."
Virgin London Marathon has pledged to donate £2 for every runner that finishes the race to The One Fund Boston, which has been set up to raise money for the victims of the bombings. Organisers expect the total donation to exceed £70,000.
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