Small charities struggling to find runners for the Virgin London Marathon have called for a service that would help them match would-be runners to empty running spots.
Several small charities contacted by Third Sector said they had found it difficult to fill many of their running slots for this year's event, which takes place on 17 April.
Some said the bulk of their places were still empty, while others said they had to reduce the amount of sponsorship they were asking runners to raise in order to fill slots.
By contrast, larger charities said their running slots were heavily oversubscribed.
David Brown, trustee director at the development charity Africa Enterprise Trust, said it had one runner for its five slots.
"Our target is £2,000, but if I had found people that were willing to raise £1,000, I would have taken them," he said. "We could have done with the money this year, but we had problems finding the people."
He added: "It would be good if there was a place for two charities to meet, one with people offering to run, one with places to spare. Logically, the marathon website would be the place.
"As it stands, they haven't got the space so they can't get the money; we haven't got the runners, so we can't get the money."
Venetia Shepherd, in charge of administration, volunteers, education and events at the conservation charity Rainforest Concern, said a marketplace for empty charity slots would be useful for small charities looking for runners.
"It would probably be of really great use to everyone, especially in view of the fact that the spaces roll over and we have 13 spaces this year, but only one filled," she said. The charity reduced its sponsorship target for each runner from £1,000 to £950 in 2009.
Helen Nevulis, senior fundraising executive at Great Ormond Street Hospital Children's Charity, said it received 450 applicants for its 50 places. "We feel that 20 to 30 per cent of our applicants have applied to other charities' websites and would be happy to run and fundraise for anyone," she said.
A spokeswoman for the London Marathon said she was unable to comment.