London Marathon runners were called “fat” and “slow” by event cleaners and marshals, according to an official race pacesetter who called their treatment “ugly, heartbreaking and not inclusive”.

Elizabeth Ayres was running the course alongside participants aiming to get round in seven-and-a-half hours on Sunday.

She said the experience was far from enjoyable as her group was left to dodge lorries after the clean-up operation started around them.

Course markings, timing mats and water stations were also taken away before they were finished, she added.

One woman reportedly received a chemical burn after being sprayed during the clean-up and another runner said she had a bruise on her thigh from a bottle lid hitting her.

London Marathon 2019 in pictures Show all 39 1 /39 London Marathon 2019 in pictures London Marathon 2019 in pictures London Marathon 2019 in pictures A gallery of the best London Marathon 2019 pictures. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures A boat passes underneath as runners cross Tower Bridge. AFP/Getty Images London Marathon 2019 in pictures London Marathon 2019 in pictures Kenya's Eliud Kipchoge leads the way during the men's elite race. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Andy Murray gets ready to start the race. PA London Marathon 2019 in pictures London Marathon 2019 in pictures Candice Brown prior to the race. PA London Marathon 2019 in pictures London Marathon 2019 in pictures Chris Evans (centre) with the Team Barbara's Revolutionaries Emma Barton, Kellie Shirley, Tanya Franks, Scott Mitchell and Natalie Cassidy. PA London Marathon 2019 in pictures London Marathon 2019 in pictures Colombia's Francisco Sanclemente after getting a puncture at the start of the men's wheelchair race. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Sanclemente inspects the damage. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Sir Mo Farah warms up. PA London Marathon 2019 in pictures London Marathon 2019 in pictures Runners prepare for the start of the race. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Charlotte Purdue (centre) at the start of the Women's London Marathon. PA London Marathon 2019 in pictures London Marathon 2019 in pictures A runner takes a photo on her phone. PA London Marathon 2019 in pictures London Marathon 2019 in pictures Runners at the start of the race. PA London Marathon 2019 in pictures London Marathon 2019 in pictures A fun runner wears a Sir Mo mask for inspiration. PA London Marathon 2019 in pictures London Marathon 2019 in pictures Sir Mo Farah (centre) at the start. PA London Marathon 2019 in pictures London Marathon 2019 in pictures Kenya's Eliud Kipchoge and Great Britain's Mo Farah. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Sir Mo makes his way at the beginning of the race. PA London Marathon 2019 in pictures London Marathon 2019 in pictures Daniel Romanchuk of the U.S. wins the men's wheelchair race, REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures A runner dressed as Spider Man. PA London Marathon 2019 in pictures London Marathon 2019 in pictures Kirsty Gallacher ahead of the race. Getty Images London Marathon 2019 in pictures London Marathon 2019 in pictures Jenni Falconer ahead of the race. Getty Images London Marathon 2019 in pictures London Marathon 2019 in pictures Switzerland's Manuela Schar wins first place in the women's wheelchair race. AP London Marathon 2019 in pictures London Marathon 2019 in pictures Switzerland's Manuela Schar celebrates. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Chris Evans at the start line. Getty Images London Marathon 2019 in pictures London Marathon 2019 in pictures Kirsty Gallacher sets off. Getty Images London Marathon 2019 in pictures London Marathon 2019 in pictures General view during the men's elite race. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Kenya's Eliud Kipchoge in action. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Japan's Tadashi Horikoshi in action during the men's para race. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Australia's Michael Roeger wins the men's para race. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Candice Brown during the Virgin London Marathon 2019. Getty Images London Marathon 2019 in pictures London Marathon 2019 in pictures Kenya's Vivian Cheruiyot in action. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Gabby Logan presenting BBC's coverage of the race. Getty Images London Marathon 2019 in pictures London Marathon 2019 in pictures Kenya's Brigid Kosgei celebrates winning the women's elite race. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Brigid Kosgei crosses the finish line. AFP/Getty Images London Marathon 2019 in pictures London Marathon 2019 in pictures Great Britain's Charlotte Purdue in action. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Brigid Kosgei wins the women's race. AP London Marathon 2019 in pictures London Marathon 2019 in pictures Great Britain's Charlotte Purdue celebrates. REUTERS London Marathon 2019 in pictures London Marathon 2019 in pictures Third place, Ethiopia's Roza Dereje (L), winner, Kenya's Brigid Kosgei (C) and second place, Kenya's Vivian Cheruiyot (R). AFP/Getty Images London Marathon 2019 in pictures London Marathon 2019 in pictures Great Britain's Hayley Carruthers falls at the end of the women's elite race. REUTERS

Marathons often have a cut-off time and this was the first year the London Marathon had taken on official pacers for finishing times slower than six hours.

Ms Ayres told the BBC’s Victoria Derbyshire programme that comments such as “if you weren’t so fat, you could run” and “this is a race, not a walk” were directed at her and other runners.

She said: “I had runners that were crying – ones saying they were going to go home and quit.”

One runner tweeted to say she was “insulted by marshall’s, sprayed with cleaning chemicals, nearly being taken out by a bin lorry and made to feel like a failure before you’ve even reached the halfway point”.

A member of March Athletic Club also raised concerns after losing track of an 80-year-old runner when the timing mats were packed away.

“We had an 80 year old runner from @AC_March running his last marathon having done the 1981 event in 2hr56,” he tweeted.

“We lost track of him due to the mats being pulled up and he got the same experience. Was a worry for all of us. Hate to say it but he deserves so much more. 100+ marathons.”

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Describing the events in a blog post that has since gone viral, Ms Ayres said: “I spent 26.2 miles being the only support for too many runners yesterday and I’m angry. I volunteered to be back at the back of the pack because it really is a lonely and unforgiving place to be but at the back of [Virgin Money London Marathon] is horrific.

“My heart breaks for every runner over 7hrs who had absolutely none of the world renowned experience.”

Event director Hugh Brasher said: “We work hard to provide the best possible experience for every runner in the London Marathon and we were very sorry to hear about the experience of Elizabeth and a small number of other runners on Sunday.

“A senior member of our team called Elizabeth yesterday to find out more and we are now looking into this in detail as part of a full investigation. We’ll be talking to the people involved to find out what happened and we’ll also be contacting the runners who were in the group being paced by Elizabeth.”

A spokesman for London Marathon Events said they were taking the reports of the comments made “very seriously” and would be launching a full investigation using “witness statements, CCTV coverage, photography and other records”.

He added that water stations have to close to a fixed schedule to allow roads to reopen but that there are a number of other ways participants can continue to get hold of water.

The organiser uses a non-caustic detergent diluted with water to clean paint off the route. It is believed a small number of runners may have come into contact with splashback from a water carrier and this will be investigated in “great detail”.