Paddington Bear has not swapped marmalade sandwiches for Marmite, his creator has insisted.
Michael Bond was reacting to criticism over the decision to use the marmalade-loving bear in a TV advert for the yeast-based spread.
And he dismissed the accusation that he was paid to write the commercial.
Paddington and Co, which owns the rights to the bear's image, gave permission for the bear to be used in the advert.
In a letter to the Times, Mr Bond dismissed a claim that he was paid a "vast sum of money" for the commercial.
'Built in stone'
"I should be so lucky - particularly since I didn't write it. In fact, I have to report that although Paddington found the sandwiches interesting, bears are creatures of habit," he wrote.
"It would require a good deal more than the combined current withdrawals from Northern Rock to wean him off marmalade, if then."
Mr Bond told BBC Radio 4's Today programme that Paddington would not give up marmalade for good.
Michael Bond based the character on a teddy he bought for his wife
"Certainly not. He never would convert," he said. "The thing about children's characters is that these things are built in stone."
Mr Bond's daughter, Karen Jankel, who is managing director of Paddington and Co, defended the company's decision.
She said people had "read the headlines and jumped to conclusions".
"Unilever wanted to encourage people to try Marmite in their sandwiches, and they were looking for a character famous for eating sandwiches," she said.
"The point of the advert is that Paddington always has marmalade in his sandwiches. He simply tries Marmite."
The advert features Paddington, wearing his usual hat and carrying his battered suitcase, sitting on a step at the side of the street.
He tries the Marmite sandwich and feeds some of it to a pigeon.
Paddington first appeared in the book A Bear Called Paddington in 1958 and became the star of a hit animated series, narrated by Sir Michael Hordern, in the 1980s.