The Spice Girls are reforming for a world tour - without Victoria Beckham

A source said: "This will be one of the biggest pop reunions of all time.

"There is a huge demand for the Spice Girls to get back together, especially with the nostalgia around the two-decade anniversary of their first release next summer.

"Mel B flew into London last month to secretly agree the plan with the other three girls. They should each make more than ten million pounds from this."

Victoria - who took part in the group's 2007-2008 reunion tour and their appearance at the London Olympics closing ceremony three years ago - still has the option to take part but insists she is too busy.

The source added to The Sun newspaper: "Victoria wishes the girls the best of luck.

"She is far too busy running her fashion brand and looking after her family to get back on a stage.

"She also feels that they left the stage on an amazing high with their Olympics performance and worries a reunion could tarnish their legacy."

Initially the group were reluctant to commit to anything without the 40-year-old star, but realised time was running out for a reunion if they didn't agree it soon.

The insider said: "For a long time they put off the idea of working any projects without her because they wanted to stay as a five-piece, but with the 20th anniversary coming up they realised it was a case of now or never."

The quartet are expected to begin negotiations with tour promoters and choose their new management team in the coming weeks.

The source said: "It will be the four girls who are making the calls about this. There is a lot to work out in terms of their schedules and priorities, but they want to be in control.

"Talks between them are continuing and there are likely to be some official decisions made when they back from their summer holidays in September or October."