The girl in the red dress with the pigtails, called Lin Miaoke, 9, and from a Beijing primary school, has become a national sensation since Friday night, giving interviews to all the most popular newspapers.

But the show's musical designer felt forced to set the record straight. He gave an interview to Beijing radio saying the real singer was a seven-year-old girl who had won a gruelling competition to perform the anthem, a patriotic song called "Hymn to the Motherland".

At the last moment a member of the Chinese politburo who was watching a rehearsal pronounced that the winner, a girl called Yang Peiyi, might have a perfect voice but was unsuited to the lead role because of her buck teeth.

So, on the night, while a pre-recording of Yang Peiyi singing was played, Lin Miaoke, who has already featured in television advertisements, was seen but not heard.

"This was a last-minute question, a choice we had to make," the ceremony's musical designer, Chen Qigang, said. "Our rehearsals had already been vetted several times - they were all very strict. When we had the dress rehearsals, there were spectators from various divisions, including above all a member of the politburo who gave us his verdict: we had to make the swap."

Mr Chen's interview gave an extraordinary insight into the control exercised over the ceremony by the Games' political overseers, all to ensure the country was seen at its best.

Officials have already admitted that the pictures of giant firework footprints which marched across Beijing towards the stadium on Friday night were prerecorded, digitally enhanced and inserted into footage beamed across the world.

Mr Chen said the initial hopefuls to sing the anthem had been reduced to ten, and one, a ten-year-old, had originally been chosen for the quality of her voice. But she, too, had fallen by the wayside because she was not "cute" enough.

"We used her to sing in all the rehearsals," Mr Chen said. "But in the end the director thought her image was not the most appropriate, because she was a little too old. Regrettably, we had to let her go."

At that point Yang Peiyi stepped up to the plate.

"The main consideration was the national interest," he said. "The child on the screen should be flawless in image, in her internal feelings, and in her expression. In the matter of her voice, Yang Peiyi was flawless, in the unanimous opinion of all the members of the team."

That was until attention turned to Yang Peiyi's teeth. Nevertheless, Mr Chen thought the end result a perfect compromise.

"We have a responsibility to face the audience of the whole country, and to be open with this explanation," he said. "We should all understand it like this: it is a question of the national interest. It is a question of the image of our national music, our national culture.

"Especially at the entrance of our national flag, this is an extremely important, an extremely serious matter.

"So we made the choice. I think it is fair to both Lin Miaoke and Yang Peiyi - after all, we have a perfect voice, a perfect image and a perfect show, in our team's view, all together."

One question remains: why was Lin Miaoke allowed to give interviews in which she lapped up the praise for her singing. Mr Chen said she might not have known that the words she was singing could not be heard. She had, in fact, only known she was going to perform at all 15 minutes beforehand.

Yang Peiyi is said to have reacted well to the disappointment. "I am proud to have been chosen to sing at all," she is reported to have said.