Osborne believes celebrities should follow the lead of businesses and select a charity of the year.
"Celebrities could commit themselves to just one charity," she said.
"It would deter other charities from making approaches and they wouldn't feel obliged to take on too much."
Osborne believes a contract would enable both parties to get the most out of the relationship.
"It wouldn't have to be written and it could even run for more than a year," she said. "The celebrity could decide how many appearances they wanted to make, and the charity could decide how to make the best use of them."
But David Piner, artist liaison co-ordinator at the British Red Cross, disagreed. "I don't believe in contracts for celebrities because they are still volunteers," he said.
"But as people become savvier, it's important for charities to build more credible relationships with their celebrity supporters."