06/08/2007 at 04:00 PM EDT
The Spice Girls are preparing for a Christmas reunion tour, sources close to the band tell PEOPLE.
"It should be happening in December," a source tells PEOPLE. "Geri [Halliwell, a.k.a. Ginger Spice] and Emma ["Baby Spice" Bunton] have been in the studio writing new material and they want to do a worldwide tour."
Rumors have circulated recently that the band would reunite for the Princess Diana memorial concert
that is to be held on Diana's birthday, July 1, to mark the 10th anniversary of her death.
"They definitely won't be performing at the Diana show. It is too soon and Emma is pregnant
," says another band insider. "But plans are afoot for later in the year. It all depends on Simon Fuller. He is the mastermind."
Fuller, 47, was the Svengali manager who turned the five-woman group into the most successful female act of the 1990s and later went on to create American Idol.
The group plans to release a greatest hits album that will include several new songs, sources tell PEOPLE. "They have a couple of new songs and one in particular is fantastic," says one recording-studio source. "It's hard to get something as pop-laden as their first hit, 'Wannabe,' but one of the new songs is heading that way and it has far more funk in it than the ballads before the band split."
Until recently, it seemed there was no hope for a reunion. "There are no plans for it at all with or without me," Melanie "Sporty Spice" Chisholm, 33, told PEOPLE
The band insider confirms that Chisholm was reluctant at first. "It's been a long time coming and the negotiations have been going on for a while," says the source. "Mel C. was the last one to come onboard as she has been pushing her solo career."
The first hint of a possible reunion came on April 22 at the baptism service
for 34-year-old Halliwell's 11-month-old daughter, Bluebell Madonna. Only L.A.-based Melanie "Scary Spice" Brown, 32, who welcomed a daughter
of her own on April 3, was absent.
Sources tell PEOPLE Fuller returned to London from Los Angeles earlier this week and is expected to craft an announcement of the reunion. Meanwhile, Victoria "Posh Spice" Beckham
has returned to California to finalize her family's move
Beckham has commissioned interior designer Kelly Hoppen, who is the stepmother of Sienna Miller
, to furnish the family's six-bedroom Beverly Hills home prior to their mid-July move. Beckham is also expected to continue filming her NBC show
during the trip.