Geri and Posh as they are now

When the girls sing out of tune on stage, the mistakes in their voices are instantaneously corrected - in less than a tenth of a second - by computer to perfect the pitch and tone. And it is this remastered "virtual voice" which belts out across the arena. The girls' vocals are altered so quickly that it will appear the resulting perfect voices are live and their own.

The system is not miming as such, because they are not just mouthing music to a backing track.

But the voices of Ginger (Geri Halliwell), Scary (Melanie Brown), Sporty (Melanie Chisholm), Baby (Emma Bunton) and Posh (Victoria Beckham) are actually changed to make them better.

"As they sing, the computer program corrects the mistakes so that the sound comes out as the desired sound - so they appear to be able to sing really well live," said an industry source. The system is being seen as a godsend for Posh - who is known for her particularly weak singing voice.

There have even been suggestions that while they are short or rehearsal time, the girls will use the computer enhancement to make sure they can perform as soon as next Sunday at the Concert for Diana at Wembley.

A Spice Girls spokesman was adamant that detailed touring logistics which would cover the use of live vocal enhancement had not yet been discussed, adding: "They all have great singing voices."