There is outrage in London about the decision by Olympic Games organisers to have the London Symphony Orchestra mime its performance at the opening ceremony.

It has emerged the world renowned orchestra will pretend to perform while a recording made six weeks ago blasts out of the stadium speakers.

Considered to be one of the best orchestras in the world, it was awarded the contract for the 2012 Games.

But when the athletes walk in to the stadium in front of a worldwide audience of 4 billion people, the orchestra will in fact be pretending.

Twitter has been abuzz with outrage.

"What a bloody joke," one person said, "The London Symphony Orchestra told to mime at games opening."

"You'll see the London Symphony Orchestra at the Olympics, but you won't hear it - how ridiculous, what a farce," another posted.

The decision was made by the London Games organising committee, which is worried about the acoustics and the uncertainties of the British weather.

"Due to the complexity of everything involved in staging the ceremonies, it's not possible for all the music in all the shows to be live," a committee spokesperson said in a statement.

"There will be live musical elements, but many of the songs will be recorded to track in advance of the shows.

"This is standard practice for an event of this scale, and the performers have no issue with it."

The music to blare out of the stadium at the opening games ceremony was recorded at the famous Abbey road studios.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 3 minutes 41 seconds 3 m 41 s Symphony Orcherstra to fake it at the Games Download 1.7 MB

Melbourne Symphony Orchestra operations director Lou Oppenheim says the decision to pre-record the music is not unreasonable.

"Performances such as the opening ceremony of the Olympic Games are incredibly complex from an operational perspective," she said.

"The inter-relationships between a whole lot of different elements, including the musical elements, the pyrotechnics, the announcements, the lighting of the cauldron - everything has to be done to split-second timing."

Ms Oppenheim says a whole lot of different things can influence what can happen with the timing which is calculated to the tenth of a second.

"The wonderful thing obviously, the audiences will be still hearing the sounds of the fabulous London Symphony Orchestra, so it's not as if they're miming to, you know, another orchestra," she said.

"But if that's what's happening I would understand that that's possibly why that might be the case."

What might come as a surprise to many is that the Sydney Symphony Orchestra mimed its performance at the opening of the Sydney Games in 2000, and the backing tape was recorded, in part, by the Melbourne Symphony Orchestra.

Ms Oppenheim says live outdoor performances are difficult to manage and it is important that nothing is left to chance.

"I think it's important that we hear orchestras in the best fantastic light and if they've actually had to make a call that that's the way they've got to do it for this, I think you know, some understanding around that and to make sure that all of the elements of the ceremony can come together as smoothly as possible," she said.