As well as the medals, which hang from a red ribbon and feature an embossed London skyline, other marathon memorabilia such as T-shirts, branded pens and even a plastic bag marking the 37th annual event are also being flogged.

One seller, who said profits from the sale will go to charities Water Aid and Save the Children, wrote: "My dad has finished the London Marathon today in 2.50.06, an absolutely cracking time.

"He has decided to sell his top and medal and donate the money to his chosen charities.

"Listing contains official finishers' 2017 London Marathon Medal. Only a few hours old."

The listing has attracted around 26 offers, with a top bid of £91.99.

Another medal seller wrote: "I'm selling this for a friend. Great collector's item."

One runner, who is auctioning off a T-shirt and medal and has attracted bids of around £80, wrote: "Ran it today but have medals from previous years so do not need this."

Other medals sold for around £70, while a red plastic bag sporting the words "Virgin Money London Marathon 2017" is being sold for £3 plus 80p postage and packaging.

The sales have been denounced on online runners' forums as "tacky", with some questioning why competitors would want to part with their hard-earned prize.

This year's event, known as the "mental health marathon" thanks to the official charity Heads Together championed by the Duke and Duchess of Cambridge and Prince Harry, saw a record 40,382 runners pound the capital's streets.