Hugh Brasher, event director for the London Marathon, said he was "very sorry" to hear of the experience of a "small number" of participants during the marathon, which took place on Sunday. A total of 42,549 runners completed the marathon, which takes in the British capital's major landmarks.
Elizabeth Ayres, one of the official pacers at the marathon, told CNN that the attitude and lack of support from officials was the most disappointing part. "The whole marathon was just horrible," she said. "I had runners that were crying." This placed a large responsibility on Ayres to motivate the competitors, who felt like no one wanted them on the track, she said.
Ayres outlined the "horrendous" treatment she and a number of other runners had received in a Facebook post and in an interview with the BBC
As a pacer, Ayres said she was asked to run the race within seven and a half hours, motivate participants and provide support to them.
She said that she had encountered a number of issues, such as no water stations being available after the third mile, clean-up operations starting while she was still running and officials insulting competitors.
Ayres told the BBC she heard insults from event workers including: "If you weren't so fat you could run faster," and "it's a race not a walk."
Ayres has a total of five marathons under her belt. She has also run the London Marathon previously, which she said usually has an up-beat, "party" atmosphere. She was expecting that again when she set off on Sunday, but told CNN that "after about a mile, we didn't have anything, apart from vehicles trying to knock us off the road," and people spraying chemicals, telling the runners to "get a move on."
"Miles 13 through to 18 were horrendous! We were sprayed with cleaning fluid and water from the clean-up vehicles, " she said in a Facebook post.
At Mile 22 the roads were opened and her group ran into traffic, Ayres said.
As the competitors reached the landmark Tower Bridge, Ayres said that they were blocked for a few minutes by sewage trucks and had to run through the vehicles.
"Tower Bridge is supposed to be where every runner gets their epic marathon shot. Not for us," she added.
According to a statement, the marathon organizers have called Ayres to find out more and the team is "now looking into this in detail as part of a full investigation."
"We were very sorry to hear about the experience of Elizabeth and a small number of other runners on Sunday," said Brasher.
He also said that his team will talk to people involved "to find out what happened" and to the runners in the group paced by Ayres.
The event has raised over £1 billion ($1.3 billion) for charity since 1981, when the first London Marathon took place. It is renowned for offering up inspiring stories.
"My heart breaks for every runner over 7 hrs who had absolutely none of the world renowned experience," she said in the Facebook post.
"It can be so easy if you're a faster runner to kind of not notice what's going on in the back," Ayres said. "They are heroes at the back, they are my heroes... It was horrible, but they got their medals. I'm so proud of them."
Ayres said she will be back at the tail end of the London Marathon 2020, to make sure people won't be treated that way again.