Personalised 'chase' letters written by London Marathon director David Bedford have recouped at least £25,000 from Golden Bond runners who failed to deliver what they pledged.
The letters were introduced after last year's event, following collaboration between Bedford and the Event Managers Forum, an informal best practice network that represents 160 charities across the UK.
Charities have often been left out of pocket by Golden Bond runners who don't send in their sponsorship money or fall short of their targets.
Gwen Pearson, events manager at the RNIB and chair of the forum, said Bedford's letter was an effective method of recovering money.
"Charities have their own individual ways of bringing in funds from errant runners, but this letter does throw some more weight behind them," she said.
She added that one "very large" charity, which she would not name, had managed to raise £8,000 through the letters.
Pearson said the forum had a close working relationship with Bedford, who, she added, shared his "wit and wisdom" at a meeting every year.